A fastener

Abstract

A fastener 100 comprises a shaft 102, comprising a first material and a pipe 112 comprising a second material. The shaft 102 has a first hole extending along a central elongate axis of the shaft from

Description

TECHNOLOGICAL FIELD Examples of the disclosure relate to a fastener. Some relate to a threaded fastener. BACKGROUND Fasteners are subject to tensile force, bend forces and rotational torque forces simultaneously, during tightening and installation and throughout their working life. The range of forces a fastener is subject to is called dynamic forces. Failure modes on critical fasteners are well documented. BRIEF SUMMARY According to various, but not necessarily all, examples there is provided a fastener comprising: a shaft, comprising a first material, the shaft comprising a first hole extending along a central elongate axis of the shaft from a first end of the shaft towards a second end of the shaft, opposite the first end; and a pipe, comprising a second material, the pipe comprising a second hole extending along the central elongate axis of the shaft from the first end of the pipe to a second end of the pipe, and provided within the first hole of the shaft, where an external surface of the pipe is attached to an internal surface of the shaft, defined by the first hole, by a third material having a lower melting point than the first material and the second material. In some but not necessarily all examples, the second material has different material characteristics to the first material. In some but not necessarily all examples, the external surface of the pipe is attached to the internal surface of the shaft by brazing, and wherein the third material is a filler material. In some but not necessarily all examples, the shaft comprises: a first externally threaded portion, extending from the first end of the shaft along at least a portion the shaft, and, optionally, a second externally threaded portion, extending along the central elongate axis of the shaft from the second end of the shaft towards the first end of the shaft. In some but not necessarily all examples, the threading is formed by rolling. In some but not necessarily all examples, an end of the first hole, opposite the first end, is rounded, and / or an end of the second hole, opposite the second end, is rounded. In some but not necessarily all examples, the fastener comprises a first insert, positioned within the second hole of the pipe. In some but not necessarily all examples, the insert provides a closed end of the Pipe- In some but not necessarily all examples, the second hole of the pipe has a rounded end; and the insert has a rounded end, shaped to fit within the rounded end of the second hole. In some but not necessarily all examples, an external surface of the insert is attached to an internal surface of the pipe, defined by the second hole, by brazing. In some but not necessarily all examples, the fastener comprises a spherical washer. In some but not necessarily all examples, the fastener comprises one or more sensors, positioned within the shaft or the pipe, the one or more sensors configured to detect at least one of: a flaw in the shaft and / or the pipe; or a change in the material properties of the shaft and / or the pipe. In some but not necessarily all examples, the fastener comprises a head provided at the second end. In some but not necessarily all examples, the head is one of: a bolt head; a substantially spherical portion; or a hex head. In some but not necessarily all examples, the first hole extends from the first end of the shaft to the second end of the shaft. In some but not necessarily all examples, the fastener comprises a third insert, provided within the first hole, wherein a cross-sectional area of the third insert decreases from an outer end, positioned on the head of the shaft, to an inner end, positioned within the first hole. In some but not necessarily all examples, the shaft comprises a third hole extending along the central elongate axis of the shaft from the second end of the shaft towards the first end of the shaft, the third hole extending along at least a portion of the shaft to form a second hollow portion of the shaft. In some but not necessarily all examples, a first hollow portion of the shaft, through which the first hole extends, and the second hollow portion of the shaft are separated by a solid portion. In some but not necessarily all examples, the fastener comprises a second pipe, comprising the second material, the second pipe comprising a fourth hole extending along a central elongate axis of the second pipe from a first end of the second pipe to a second end of the second pipe, and provided within the third hole of the shaft, wherein an external surface of the second pipe is attached to an internal surface of the shaft, defined by the third hole, by the third material. In some but not necessarily all examples, the fastener comprises a second insert, positioned within the fourth hole of the pipe. The fastener provides multiple advantages over traditional fasteners, in particular solid section fasteners such as bolts or studs. The fastener provides reduced notch sensitivity due to lower concentration of forces in a single thread form, because the provision of the pipe enables distribution of forces across the fastener, and because the pipe contains no notch sensitivities having no thread form. In particular, the fastener spreads pre-load and cyclic forces across multiple thread forms. The fastener inhibits propagation of flaws through the shaft, because the flaws may not propagate through the third material or through the pipe. If a flaw does propagate, it must propagate around the pipe, instead of directly across the shaft (as occurs in a solid section fastener), inhibiting failure due to flaw propagation. The fastener provides improved fatigue strength, bend strength and dynamic strength, as well as providing a significantly increased load transfer stress area, due to the improved properties of the hollow pipe over a solid section, as well as the brazed joint between the hollow pipe and the shaft. In addition to the improved strength, the fastener is also lighter than a solid section fastener. Because the fastener comprises two components brazed together, it provides damping and shock absorbing properties, which have particular benefits for use in structures in areas with high seismic activity. Because of the improved characteristics of the fastener, the fastener requires less maintenance than a traditional fastener, increasing service life of the fastener and asset life of structures in which the fastener is employed. The fastener also therefore provides significantly increased safety over traditional fasteners. Further, the fastener prevents, or dramatically slows down, immediate failures, giving time for sensor technology to warn an operator to cease work in case of an impending failure event, saving lives and protecting high value assets According to various, but not necessarily all, examples there is provided a fastener safety detection system, comprising: a fastener; and means for providing an alert in response to a detection of at least one of: a flaw in the shaft and / or the pipe; or a change in the material properties of the shaft and / or the pipe. According to various, but not necessarily all, examples there is provided a method of manufacturing a fastener, comprising: providing a shaft, comprising a first material, the shaft comprising a first hole extending along a central elongate axis of the shaft from a first end of the shaft towards a second end of the shaft, opposite the first end; providing a pipe, comprising a second material, comprising a second hole extending along the central elongate axis of the pipe from the first end of the pipe to the second end of the pipe, wherein providing the pipe comprises extruding the pipe; providing the pipe within the first hole of the shaft; and attaching an external surface of the pipe to an internal surface of the shaft, defined by the first hole, using brazing, such that the external surface of the pipe is attached to the internal surface of the shaft by a third material having a lower melting point than the first material and the second material. In some but not necessarily all examples, the direct product of the method is a fastener. In some but not necessarily all examples, the fastener is a fastener as described above. According to various, but not necessarily all, examples there is provided a fastener, comprising: a shaft, comprising a first material, wherein a first portion of the shaft, extending from a first end of the shaft towards a second end of the shaft, has a larger diameter than a second portion of the shaft, extending form the second end of the shaft towards the first end of the shaft; and a sleeve, comprising a second material, the sleeve comprising an externally threaded portion, and a hole extending along a central elongate axis of the sleeve from a first end of the sleeve to the second end of the sleeve, wherein the second portion of the shaft is provided within the hole of the sleeve, and an external surface of the second portion of the shaft is attached to an internal surface of the sleeve, defined by the hole, by a third material having a lower melting point than the first material and the second material. In some, but not necessarily all, examples, an external diameter of the sleeve is equal, or substantially equal, to the diameter of the first portion of the shaft. In some, but not necessarily all, examples, the first portion and the second portion are separated by a third portion, a diameter of the third portion decreasing from a first end of the third portion, adjacent the first portion, to a second end of the third portion, adjacent the second portion. In some, but not necessarily all examples, the second material has different material characteristics to the first material. In some, but not necessarily all, examples, the external surface of the second portion of the shaft is attached to the internal surface of the sleeve by brazing, and the third material is a filler material. In some, but not necessarily all, examples, the externally threaded portion is formed by rolling. According to various, but not necessarily all, examples, there is provided a fastener safety detection system, comprising a fastener; one or more sensors; and means for providing an alert in response to a detection of at least one of: a flaw in the shaft and / or the pipe; or a change in the material properties of the shaft and / or the pipe. According to various, but not necessarily all, examples, there is provided a method of manufacturing a fastener, comprising: providing a shaft, comprising a first material, wherein a first portion of the shaft, extending from a first end of the shaft towards a second end of the shaft, has a larger diameter than a second portion of the shaft, extending form the second end of the shaft towards the first end of the shaft; [roviding a sleeve, comprising a second material, the sleeve comprising an externally threaded portion, and a hole extending along a central elongate axis of the sleeve from a first end of the sleeve to the second end of the sleeve; providing the second portion of the shaft within the hole of the sleeve; and attaching an external surface of the second portion of the shaft to an internal surface of the sleeve, defined by the hole, using brazing, such that the external surface of the second portion of the shaft is attached to the internal surface of the sleeve by a third material having a lower melting point than the first material and the second material. In some, but not necessarily all, examples, the direct product of the method is a fastener. According to various, but not necessarily all, embodiments there is provided an apparatus comprising means for performing at least part of one or more methods described herein. The description of a function and / or action should additionally be considered to also disclose any means suitable for performing that function and / or action. Functions and / or actions described herein can be performed in any suitable way using any suitable method. According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims. While the above examples of the disclosure and optional features are described separately, it is to be understood that their provision in all possible combinations and permutations is contained within the disclosure. It is to be understood that various examples of the disclosure can comprise any or all the features described in respect of other examples of the disclosure, and vice versa. Also, it is to be appreciated that any one or more or all the features, in any combination, may be implemented by / comprised in / performable by an apparatus, a method, and / or computer program instructions as desired, and as appropriate. The description of a function should additionally be considered to also disclose any means suitable for performing that function BRIEF DESCRIPTION Some examples will now be described with reference to the accompanying drawings in which: FIG. 1 shows an example bolted joint; FIG. 2 shows an example fastener; FIG. 3 shows an example fastener; FIG. 4 shows an example fastener; FIG. 5 shows an example fastener; FIG. 6 shows an example fastener; FIG. 7 shows an example fastener; FIG. 8 shows an example fastener; FIG. 9 shows an example fastener; FIG. 10 shows an example fastener; FIG. 11 shows an example fastener; FIG. 12 shows an example fastener; FIG. 13 shows an example fastener; FIGs. 14A and 14B show example fastener heads; FIG. 15 shows an example fastener; FIG. 16 shows an example fastener; FIG. 17 shows an example fastener; FIG. 18 shows an example method; FIG. 19 shows an example method; FIGs. 20A - 20C show example methods; FIG. 21 shows an example method; FIGs 22A and 22B show example methods; FIG. 23 shows an example method; FIG. 24 shows an example method; FIG. 25 shows an example method; FIG. 26 shows an example fastener; FIG. 27 shows an example method; and FIG. 28 shows an example method. The figures are not necessarily to scale. Certain features and views of the figures can be shown schematically or exaggerated in scale in the interest of clarity and conciseness. For example, the dimensions of some elements in the figures can be exaggerated relative to other elements to aid explication. Similar reference numerals are used in the figures to designate similar features. For clarity, all reference numerals are not necessarily displayed in all figures. DETAILED DESCRIPTION Threaded fasteners are employed around the world in a wide range of industries. A typical threaded fastener comprises a head form or drive and a plain shank which is partially or fully threaded, or a plain shank which is fully threaded with no head form. Such fasteners are provided at a variety of lengths, using various materials from mild steel to super alloys, and having various strength grades. Fasteners are typically available with diameters of M10 up to M300 and larger. Fasteners are subject to tensile forces, bend forces and rotational torque forces simultaneously, during tightening and installation and throughout their working life. The range of forces a fastener is subject to is called dynamic forces. Failure modes on critical fasteners are well documented. Failure of fasteners used in, for example, construction of skyscrapers, bridges, cranes, wind turbines and many more may have significant consequences including fatality, injury, damage to buildings and machinery, and financial losses. The thread on a threaded fastener is a helical thread form. Regardless of the manufacturing method used to produce the thread, a helical thread typically has a “V” shape with a small root radius. “V” thread profiles are notch sensitive stress concentration areas, meaning that large stress concentrations form at the threads. Said stress concentrations are the main cause of failure in threaded fasteners. FIG. 1 illustrates an example bolted joint, comprising a bolt 1, a nut 2 and an object to be joined 3. The last full thread form 4 on the bolt forward of the nut face 5 and the joint face 6 experiences the largest concentration of pre-load forces along with any dynamic forces acting on the fastener. Forces concentrated in the root of this thread form may initiate a major stress concentration, from which a flaw or crack can initiate. The flaw or crack may propagate deeper into the solid section of the fastener due to continued stretching pre-load forces. Propagation may accelerate into the solid section and eventually cause failure of the fastener, whose reduced cross-sectional area can no longer support the pre-load forces. Failure of one fastener, especially a sudden failure, causes the forces previously applied to said fastener to be transferred to other fasteners. This can cause rapid 10 “domino-type” failure of fasteners, causing the structure supported by the fasteners to collapse. Further, high strength fasteners for high load applications such as a slewing ring for a crane are less ductile than lower-grade alternatives. A flaw in such materials may have an instantaneous failure time, so no warning or sensor loading technology can be fast enough to alert an operator or other users of the structure such that they may reach safety before failure. The present invention provides a fastener that inhibits the most common causes of failure in threaded fasteners. One example embodiment uses a dampening, load transferring, pre-load maintaining, redundant thread transfer mechanism to inhibit immediate failure of a fastener, by incorporating a vacuum brazed or continuous process brazed thick wall pipe along its entire or partial axial length in varying materials. This provides for more time for an advanced sensor technology system to warn the operator or users before catastrophic failure occurs. Further advantages are also provided. The below description describes, and the FIGs illustrate, various examples of a fastener comprising: a shaft, comprising a first material, the shaft comprising a first hole extending along a central elongate axis of the shaft from a first end of the shaft towards a second end of the shaft, opposite the first end; and a pipe, comprising a second material, the pipe comprising a second hole extending along the central elongate axis of the shaft from a first end of the pipe to a second end of the pipe, and provided within the first hole of the shaft, where an external surface of the pipe is attached to an internal surface of the shaft, defined by the first hole, by a third material having a lower melting point than the first material and the second material. In preferred embodiments, the external surface of the pipe is attached to the internal surface of the shaft by brazing. In such examples, the third material is a filler material. Attaching the pipe to the shaft by brazing provides a strong joint. FIG. 2 illustrates an example fastener 100. The fastener 100 comprises a shaft 102 comprising a first material. In FIGs 2-17, the shaft 102 is illustrated by diagonal line shading. The shaft 102 comprises a first hole 104 extending along a central elongate axis A of the shaft 102 from a first end 108 of the shaft 102 towards a second end 110 of the shaft 102, opposite the first end 108. The first hole 104 is therefore a central hole. In some, but not necessarily all, examples, the shaft 102 and the first hole 104 have a circular cross-section. The first hole 104 has a constant or substantially constant cross-section such that a hollow portion of the shaft 102, through which the first hole 104 extends, has a constant or substantially constant cross-section. A solid portion of the shaft 102, through which no hole extends, may also have a constant or substantially constant cross-section. In the example of FIG. 2, the first hole 104 extends from the first end 108 of the shaft 102 to the second end 110 of the shaft 102; in other words, the first hole 104 extends the entire length of the shaft 102. The hollow portion therefore comprises the whole of the shaft 102. The shaft 102 may also be referred to as a shank or a plain portion. In some, but not necessarily all, examples, the first material comprises metal, for example, any of: stainless steels; duplex and super duplex; nickel alloys; titanium; carbon steel; mild steel; brass; copper; aluminium; or any other suitable metal. In some, but not necessarily all, examples, the shaft 102 is formed by rolling down an ingot into bar lengths and cut to the desired size. In such examples the shaft 102 is described as a wrought condition. The fastener 100 comprises a pipe 112 comprising a second material. In FIGs 2 -17, the pipe 112 is illustrated by dotted shading. The pipe 112 comprises a second hole 114 extending along the central elongate axis of the shaft 102 from a first end 116 of the pipe 112 to a second end 118 of the pipe 112, opposite the first end 116. The central elongate axis A of the shaft 102 and a central elongate axis of the pipe 112 are co-linear, such that the second hole 114 extends along the central elongate axis of the pipe 112. In some, but not necessarily all, examples, the pipe 112 and the second hole 114 have a circular cross-section. The second hole 114 has a constant or substantially constant cross-section such that a first portion of the pipe 112, through which the second hole 114 extends, has a constant or substantially constant cross-section. In some, but not necessarily all, examples, the second material comprises metal. The second material may be the same material as the first material or may be a different material to the first material. In some, but not necessarily all, examples, the second material has different characteristics to the first material. For example, one or more of the following characteristics of the second material may be different to corresponding characteristics of the first material: ductility; strength; malleability; yield strength; toughness; elasticity; plasticity; hardness; brittleness or any other material characteristic. Further, the second material may have a different grain flow to the first material. In some, but not necessarily all, examples, the grain flow of the second material is longer than the grain flow of the first material. A longer grain flow provides improved ability of the second material to withstand sudden shocks and dynamic forces. The pipe 112 is provided within the first hole 104 of the shaft 102. An external surface of the pipe 112 is attached to an internal surface of the shaft 102, defined by the first hole 104, by a third material 120 having a lower melting point than the first material and the second material. In FIGs 2-17, the third material is illustrated with solid black shading. In some, but not necessarily all, examples, the pipe 112 and the first hole 104 are sized to have a clearance fit or an interference fit such that the third material 120 may flow by capillary action into gaps between the external surface of the pipe 112 and the internal surface of the shaft 102. An interference fit enables flowing of the third material 120 when the fastener 100 is heated during brazing. This provides for full gap fill coverage by the third material 120. The shape of the pipe 112 and the second hole 114 provides advantageous characteristics. The pipe 112 has a stronger bend strength than that of a solid section having no hole. Under bending load, the compressive surface and the tensile surface at the outer diameter of a pipe 112 are further apart than that of a solid section, causing reduced stress concentrations in the pipe 112 relative to the solid section. Under torsional load, a pipe 112 distributes the load along its entire axis and length across a large cross-sectional area. This is advantageous relative to headed fasteners, which to a greater extent rely on an under-head radius to withstand said forces. In some, but not necessarily all, examples, the pipe 112 is formed by extrusion. Extrusion comprises heating up a billet of material and forcing it hydraulically into a die to produce the required shape. In some such examples, the second hole 114 is an extruded bore. In some such examples, the pipe 112 is machined after extrusion. In some, but not necessarily all, examples, the pipe 112 is formed entirely by machining. In some, but not necessarily all, examples, the external surface of the pipe 112 is attached to the internal surface of the shaft 102 by brazing. In some, but not necessarily all, examples, the brazing comprises vacuum furnace brazing. In other examples, the brazing comprises continuous process brazing. In some examples, the third material 120 is a filler material. The third material 120 is different to the first material and the second material. The third material 120 may comprise any material suitable for use as a brazing filler material. In some, but not necessarily all, examples, the third material 120 comprises any of: copperfusion; silver-nickel; silver-copper; phosphorous-nickel; copper-zinc; copper-phosphorous; nickel-copper; titanium-based filler materials; palladium-based filler materials; cobalt-based filler materials; stainless steel-based filler materials; or tungsten-based filler materials. Brazing is distinct from soldering in that a brazed joint or bond is a fusion joint or bond having an intermolecular bond as strong as or stronger than the materials it is joining. A brazed joint or bond does not affect the material strength of the components being joined together. In contrast, a soldered joint or bond is weaker than the metals it joins and is a non-fusion, non-intermolecular bond. Brazing is carried out at a higher temperature than soldering. In some, but not necessarily all, examples, the step of brazing is followed by a restorative heat treatment. This restores, where necessary, the mechanical properties of the joined materials. In some, but not necessarily all, examples, the fastener 100 comprises one or more sensors (not illustrated). The sensors may be provided within the first hole 104 of the shaft 102 or the second hole 114 of the pipe 112, or on an outer surface of the shaft 102, for example. The sensors are configured to detect at least one of: a flaw in the shaft 102 and / or the pipe 114; or a change in the material properties of the shaft 102 and / or the pipe 112. In other embodiments, the sensors are configured to detect different signs that the fastener is likely to fail. The fastener 100, comprising one or more sensors, may be provided as part of a fastener safety detection system. The fastener safety detection system also comprises means for providing an alert in response to a detection of at least one of: a flaw in the shaft 102 and / or the pipe 112; or a change in the material properties of the shaft 102 and / or the pipe 112. The means for providing an alert may comprise a single alerting means, provided, for example, in a structure in which the fastener 100 is employed such as a crane, bridge or skyscraper. The means for providing an alert may therefore, for example, alert a crane operator that there is a risk of joint failure, enabling the operator to cease work and evacuate the crane before failure occurs. The means for providing an alert may comprise multiple alerting means, provided, for example, in the structure in which the fastener 100 is employed and additionally in other positions, such as an overseer’s office for a building site, in local emergency service buildings, or in other positions where knowledge of a risk of joint failure is advantageous. FIG. 3 illustrates an example fastener 100. The example fastener 100 of FIG. 3 is the same as the example fastener 100 of FIG. 2, except for the differences set out below. In some, but not necessarily all, examples, the shaft 102 comprises an externally threaded portion 302. The externally threaded portion 302 extends from the first end 108 of the shaft 102 along a portion of the shaft 102 towards the second end 110 of the shaft 102. In the example of FIG. 3, the externally threaded portion 302 extends approximately a third of the length of the shaft 102; it will be appreciated that the externally threaded portion 302 may extend a longer or shorter distance along the shaft 102, including along the entirety of the shaft 102 from the first end 108 of the shaft to the second end 110 of the shaft. In some, but not necessarily all, examples, the externally threaded portion 302 is formed by rolling. In some such examples the rolling is performed after heat treatment of the shaft 102. A rolled thread form has a greater fatigue life than that of a cut thread. In some, but not necessarily all, examples, the fastener 100 comprises a head 304 provided at the second end 110 of the shaft. In some such examples, the head 304 is formed integrally with the shaft 102 as a single part. In the example of FIG. 3, the head 304 is a bolt head. In some, but not necessarily all, examples, the first hole 104 extends through the head 304. In some such examples, the pipe 112 and the second hole 114 also extend through the head 304. FIG. 4 illustrates another example fastener 100. The example fastener 100 of FIG. 4 is the same as the example fastener 100 of FIG. 3, except for the differences set out below. In the fastener 100 of FIG. 4, the first hole 104 is a part-hole, that is, the first hole extends from the first end 108 of the shaft 102 towards the second end 110 of the shaft 102 along a portion, but not all, of the shaft 102. In the example of FIG. 4, the first hole 104 extends approximately a third of the length of the shaft 102; it will be appreciated that the first hole 104 may extend a longer or shorter distance along the shaft 102. The portion of the shaft 102 through which the first hole 104 extends is a hollow portion of the shaft 102. In some, but not necessarily all, examples, an end of the first hole 104, opposite the first end 108 of the shaft 102, is rounded. In some, but not necessarily all examples, the first hole 104 is a blind hole. In the example of FIG. 4, the hollow portion and the externally threaded portion 302 extend substantially the same distance along the shaft 102 from the first end. In other examples, the hollow portion may extend a longer or shorter distance along the shaft 102 from the first end than the externally threaded portion 302. FIG. 5 illustrates another example fastener 100. The example fastener 100 of FIG. 5 is the same as the example fastener 100 of FIG. 4, except for the differences set out below. In the example of FIG. 5, the fastener 100 comprises an insert 502. The insert 502 comprises a fourth material. In FIGs 5-17, the insert 502 is illustrated by square hatched shading. In some, but not necessarily all, examples, the fourth material is the same material as the first material and / or the second material. In other examples, the fourth material is a different material to the first material and / or the second material. The insert 502 is positioned within the second hole 114 of the pipe 112. In some, but not necessarily all, examples, an external surface of the insert 502 is attached to an internal surface of the pipe 112, defined by the second hole 114, by a fifth material 504 having a lower melting point than the second material and the fourth material. In some, but not necessarily all, examples, the insert 502 and the second hole 114 are sized to have a clearance fit or an interference fit such that the fifth material 504 may flow by capillary action into gaps between the external surface of the insert 502 and the internal surface of the pipe 112. An interference fit enables flowing of the fifth material 504 when the fastener 100 is heated during brazing. This provides for full gap fill coverage by the fifth material 504. In some, but not necessarily all, examples, the external surface of the insert 502 is attached to the internal surface of the pipe 112 by brazing. In some, but not necessarily all, examples, the brazing comprises vacuum furnace brazing or continuous process brazing. In some, but not necessarily all, examples, the fifth material 504 is a filler material. The fifth material 504 may be the same material as the third material 120 or may be a different material to the third material 120. The fifth material 504 may comprise any material suitable for use as a brazing filler material, such as the materials indicated for the third material 120. The insert 502 thus provides a closed end of the pipe 112 at the first end 116 of the pipe 112. In some, but not necessarily all, examples, the insert 502 has a rounded end shaped to fit within the rounded end of the first hole 104 of the shaft 102. FIG. 6 illustrates an example fastener 100. The example fastener of FIG. 6 is the same as the example fastener 100 of FIG. 3, except for the differences set out below. The fastener 100 of FIG. 6 comprises two externally threaded portions 302. The externally threaded portions are externally threaded portions 302 as described above. The first externally threaded portion 302 extends from the first end 108 of the shaft 102 as described with respect to FIG. 4. The second externally threaded portion 302 extends from the second end 110 of the shaft 102 along a portion of the shaft 102 towards the first end 108 of the shaft 102. In the example of FIG. 6, the second externally threaded portion 602 extends approximately a third of the length of the shaft 102; it will be appreciated that the second externally threaded portion 602 may extend a longer or shorter distance along the shaft 102. FIG. 7 illustrates an example fastener 100. The example fastener 100 of FIG. 7 is the same as the example fastener 100 of FIG. 4, except for the differences set out below. In the example of FIG. 7, the fastener 100 comprises two externally threaded portions 302, 602, as described with reference to FIG. 6. In the example of FIG. 7, the shaft 102 comprises two holes (referred to as the first hole 104 and the third hole 706). The first hole and the third hole are the same as the first hole 104 as described above. In the example of FIG. 7, first hole extends from the first end 108 of the shaft 102 as described with respect to FIG. 4. The third hole extends along the central elongate axis of the shaft 102 from the second end 110 of the shaft 102 towards the first end 108. The shaft 102 thus comprises a first hollow portion, through which the first hole extends, and a second hollow portion, through which the third hole extends. The first hollow portion and the second hollow portion are separated by a solid portion. Thus, the first hole and the third hole are part-holes. In the example of FIG. 6, the second hollow portion and the second externally threaded portion 602 extend substantially the same distance along the shaft 102 from the second end. In other examples, the second hollow portion may extend a longer or shorter distance along the shaft 102 from the second end than the second externally threaded portion 602. In the example of FIG. 7, the fastener 100 comprises two pipes 112 as described above. The first pipe 112 is provided within the first hole and extends from the first end 108 of the shaft 102 towards the second end 110 of the shaft 102, as described with respect to FIG. 4. The second pipe 112 is provided within the third hole and extends from the second end 110 of the shaft 102 towards the first end 108 of the shaft 102. The first pipe 112 and the second pipe 112 comprise second and fourth holes 114, 708 respectively. The second hole 114 and the fourth hole 708 are the same as the second hole 114 as described above. FIG. 8 illustrates an example fastener 100. The example fastener 100 of FIG. 8 is the same as the example fastener 100 of FIG. 7, except for the differences set out below. In the example of FIG. 8, the fastener 100 comprises two inserts 502,802 as described with respect to FIG. 5. The first insert 502 is provided within the second hole 114 of the first pipe 112 as described above. The second insert 802 is provided within the fourth hole of the second pipe 112. FIG. 9 illustrates an example fastener 100. The example fastener 100 of FIG. 9 is the same as the example fastener 100 of FIG. 3, except for the differences set out below. In the example of FIG. 9, instead of a bolt head, the head 304 is a substantially spherical portion. In some, but not necessarily all, examples, the substantially spherical portion is formed with the shaft 102 by hot forging, then fine turned. FIG. 10 illustrates an example fastener 100. The example fastener 100 of FIG. 10 is the same as the example fastener 100 of FIG. 4, except for the differences set out below. In the example of FIG. 10, instead of a bolt head, the head 304 is a substantially spherical portion as described with reference to FIG. 9. FIG. 11 illustrates an example fastener 100. The example fastener 100 of FIG. 11 is the same as the example fastener 100 of FIG. 10, except for the differences set out below. In the example of FIG. 11, the fastener 100 comprises an insert 502 as described with reference to FIG. 5. FIG. 12 illustrates an example fastener 100. The example fastener 100 of FIG. 12 is the same as the example fastener 100 of FIG. 3, except for the differences set out below. In the example of FIG. 12, instead of a bolt head, the fastener 100 comprises a head 304 as illustrated in FIG. 14A or in FIG. 14B. The fastener 100 may comprise a different head 304 to those illustrated in FIGs 14A and 14B, or may comprise no head. The head 304 illustrated in FIG. 14A is a hex head. The head 304 illustrated in FIG. 14B is a substantially circular head comprising a hexagonal cavity and drive portions. The drive portions enable rotation of the fastener 100 about the central elongate axis of the shaft 102. In addition to the pipe 112, the fastener 100 of FIG. 12 comprises a third insert and a fourth insert. The third insert and the fourth insert will be referred to as a first flex arrester 1202 and a second flex arrester 1204 respectively, to distinguish them from the inserts 502 described above. The first flex arrester 1202 and the second flex arrester 1204 comprise a sixth material. In some, but not necessarily all, examples, the sixth material is the same material as the first material and / or the second material and / or the third material 120. In other examples, the sixth material is a different material to the first material and / or the second material and / or the third material 120. The first flex arrester 1202 is provided within the first hole 104 of the shaft 102. The first flex arrester 1202 extends from the first end 108 of the shaft 102 towards the second end 110 of the shaft 102. The second flex arrester 1204 is also provided within the first hole 104 of the shaft 102. The second flex arrester 1204 extends from the second end 110 of the shaft 102 towards the first end 108 of the shaft 102. As illustrated in FIG. 12, the second flex arrester 1204 may extend past the second end 110 of the shaft 102. In some such examples, a cross-sectional area of the second flex arrester 1204 decreases from an outer end, positioned on the head of the fastener, to an inner end within the first hole 104 of the shaft 102. In some, but not necessarily all, examples, the second flex arrester 1204 is positioned within a cavity of the head 304, as illustrated in FIGs 14A and 14B. An external surface of the first and / or second flex arrester 1202, 1204 is attached to the internal surface of the shaft 102 by a seventh material 1206 having a lower melting point than the first material and the sixth material. In some, but not necessarily all, examples, a flex arrester 1202, 1024 and the first hole 104 are sized to have a clearance fit or an interference fit such that the seventh material 1206 may flow by capillary action into gaps between the external surface of the flex arrester and the internal surface of the shaft 102. An interference fit enables flowing of the seventh material when the fastener 100 is heated during brazing. This provides for full gap fill coverage by the seventh material. In some, but not necessarily all, examples, the external surface of the flex arrester(s) 1202, 1204 is attached to the internal surface of the pipe 112 by brazing. In some, but not necessarily all, examples, the brazing comprises vacuum furnace brazing or continuous process brazing. In some, but not necessarily all, examples, the seventh material 1206 is a filler material. The seventh material may be the same material as the third material 120 or may be a different material to the third material 120. The seventh material may comprise any material suitable for use as a brazing filler material, such as the materials indicated for the third material 120. The insert thus provides a closed end of the pipe 112 at the first end 116 of the pipe 112. FIG. 13 illustrates an example fastener 100. The example fastener 100 of FIG. 13 is the same as the example fastener 100 of FIG. 12, except for the differences set out below. In the example of FIG. 13, the fastener 100 comprises a single flex arrester 1202. The flex arrester 1202 is provided within the pipe 112. The flex arrester 1202 extends from the first end 116 of the pipe 112 to the second end 118. In the example of FIG. 13, the flex arrester 1202 extends past the second end 110 of the shaft 102. FIG. 15 illustrates a partial view of an example fastener 100. The fastener 100 may be any fastener 100 as described above. In the example of FIG. 15, the fastener 100 further comprises a nut 1502. The nut 1502 comprises an internally threaded portion configured to engage with an externally threaded portion 302 of the shaft 102. FIG. 16 illustrates an example fastener 100. The example fastener 100 of FIG. 16 is the same as the example fastener 100 of FIG. 15, except for the differences set out below. In the example of FIG. 16, the fastener 100 comprises a spherical washer 1602. In some examples, the shaft 102 and pipe 112 have a concave cut-out (not illustrated) that is shaped to receive a convex side of the spherical washer 1602. FIG. 17 illustrates an example fastener 100. The example fastener 100 of FIG. 17 is the same as the example fastener 100 of FIG. 15, except for the differences set out below. In the example of FIG. 17, the fastener 100 comprises a locknut 1720. In some examples, the shaft 102 and pipe 112 have a concave cut-out (not illustrated) that is shaped to receive a convex side of the locknut 1720. FIGs 18-25 illustrate examples of methods 1800, 1900, 2000, 2040 and 2060, and sub-methods 2100, 2200, 2250, 2300. Method 1800, illustrated in FIG. 18, is a method of manufacturing a fastener. Method 1800 comprises, at block 1802, providing a shaft. The shaft comprises a first material. The shaft further comprises a first hole extending along a central elongate axis of the shaft from a first end of the shaft to a second end of the shaft, opposite the first end. In some, but not necessarily all, examples, block 1802 comprises sub-method 2100, illustrated in FIG. 21. At block 2102, sub-method 2100 comprises producing one or more holes in the shaft. The shaft may be, for example, a bolt blank, a cylindrical blank or another suitable shaft. In some examples, producing the one or more holes comprises boring a part-hole or a through-hole into the shaft from the first end of the shaft towards the second end of the shaft. In some examples, producing the one or more holes further comprises boring a second part-hole into the shaft from the second end of the shaft towards the first end of the shaft. Other methods of providing the hole(s) may be used. In some, but not necessarily all, examples, sub-method 2100 comprises, at block 2104, producing an externally threaded portion, extending from the first end of the shaft towards the second end of the shaft. In some, but not necessarily all, examples, block 2104 further comprises producing a second threaded portion extending from the second end of the shaft towards the first end. In some, but not necessarily all, examples, producing externally threaded portions comprises rolling the externally threaded portions. Returning to FIG 18, method 1800 comprises, at block 1804, providing one or more pipes. The one or more pipes comprise a second material. The one or more pipes comprise a second hole extending along the central elongate axis of the shaft from the first end of the pipe to a second end of the pipe. In some examples in which the shaft comprises one hole, the method 1800 comprises providing one pipe. In some examples in which the shaft comprises two holes, the method 1800 comprises providing two pipes. In some, but not necessarily all, examples, block 1804 comprises sub-method 2200 (illustrated in FIG. 22A) or sub-method 2250 (illustrated in FIG. 22B). Sub-method 2200 comprises, at block 2202, extruding the one or more pipes. Extrusion comprises heating up a billet of material and forcing it hydraulically into a die to produce the required shape. In some, but not necessarily all, examples, sub-method 2200 comprises, at block 2204, machining the one or more pipes. The machining of block 2204 may be considered a ‘finishing’ step, to produce the required shape and dimensions of the pipe(s) to a narrower tolerance than is possible by extrusion alone. Alternatively to sub-method 2200, block 1804 may comprise sub-method 2250. Sub-method 2250 comprises, at block 2252, machining the one or more pipes. The machining of block 2252 may produce the one more pipes from blanks. Referring back to FIG 18, method 1800 comprises, at block 1806, attaching the one or more pipes to the shaft. The pipe(s) is provided within the first hole of the shaft. An external surface of the pipe(s) is attached to an internal surface of the shaft, defined by the first hole, by a third material having a lower melting point than the first material and the second material. In some, but not necessarily all, examples, block 1806 comprises sub-method 2300 as illustrated in FIG 23. At block 2302, sub-method 2300 comprises copper plating the shaft and / or the one or more pipes. At block 2304, sub-method 2300 comprises positioning the one or more pipes in respective one or more holes in the shaft. In some, but not necessarily all, examples, the pipe(s) and the holes are sized to have a clearance fit such that a third material may flow by capillary action into gaps between the external surface of the pipe(s) and the internal surface of the shaft. At block 2306, sub-method 2300 comprises brazing the pipe(s) into the hole(s) 104 of the shaft. The step of brazing comprises providing the third material. The third material is provided into gaps between the external surface of the pipe(s) and the internal surface of the shaft. The step of brazing further comprises heating the fastener. In some, but not necessarily all examples, block 2304 comprises vacuum furnace brazing. In other examples, block 2304 comprises continuous process brazing. Alternatively, other known methods of brazing may be used. The brazing may be carried out with a straight or plain diameter or may be carried out on a helical wave pattern. Brazing on a helical wave pattern provides an improved joint interface, in which the cross-sectional area is larger than that of a straight brazed surface. This provides a joint with increased bond strength at the same linear dimensions. In some, but not necessarily all, examples, block 2304 is followed by block 2306. At block 2307, sub-method 2300 comprises heat treating the fastener. There is therefore provided a method 1800 comprising: providing a shaft; providing a pipe; and attaching the pipe to the shaft. In some, but not necessarily all, examples, method 1800 is followed by method 1900. Method 1900 is illustrated in FIG. 19. Method 1900 comprises, at block 1902, providing one or more inserts. The insert(s) comprise a fourth material. Method 1900 comprises, at block 1904, attaching the one or more inserts to the pipe(s). The insert(s) are provided within the second hole(s) of the pipe. An external surface of the insert(s) is attached to an internal surface of the pipe(s), defined by the second hole(s), by a fifth material having a lower melting point than the second material and the fourth material. In some, but not necessarily all, examples, block 1904 comprises sub-method 2400, as illustrated in FIG. 24. At block 2402, sub-method 2400 comprises positioning the one or more inserts in respective one or more second holes in the pipe(s). In some, but not necessarily all, examples, the insert(s) and the second hole(s) are sized to have a clearance fit such that the fifth material may flow by capillary action into gaps between the external surface of the insert(s) and the internal surface of the pipe(s). At block 2404, sub-method 2400 comprises brazing the pipe(s) into the second hole(s) of the pipe(s). The step of brazing comprises providing the fifth material. The fifth material is provided into gaps between the external surface of the insert(s) and the internal surface of the second hole of the pipe(s). The step of brazing further comprises heating the fastener 100. In some, but not necessarily all examples, block 2404 comprises vacuum furnace brazing. In other examples, block 2404 comprises continuous process brazing. Alternatively, other known methods of brazing may be used. In some, but not necessarily all, examples, block 2404 is followed by block 2406. At block 2406, sub-method 2400 comprises heat treating the fastener. There is therefore provided a method comprising: providing one or more inserts; and attaching the one or more inserts to one or more pipes. In some, but not necessarily all, examples, the inserts are flex arresters as described above. The flex arresters comprise a sixth material. In some examples in which the inserts are flex arresters, block 1904 comprises, as an alternative to sub-method 2400, sub-method 2500 (illustrated in FIG. 25). Sub-method 2500 comprises, at block 2502, positioning the one or more flex arresters in the hole(s) of the shaft. In some, but not necessarily all, examples, a first flex arrester extends from the first end of the shaft towards the second end of the shaft, and a second flex arrester extends from the second end of the shaft towards the first end of the shaft. In some, but not necessarily all, examples, the second flex arrester extends past the second end of the shaft, such that a cross-sectional area of the second flex arrester decreases from an outer end, positioned outside the shaft, to an inner end within the first hole of the shaft. In some, but not necessarily all, examples, one flex arrester is provided. The flex arrester extends from the second end of the shaft towards the first end of the shaft. In some, but not necessarily all, examples, the second flex arrester extends past the second end of the shaft, such that a cross-sectional area of the second flex arrester decreases from an outer end, positioned outside the shaft, to an inner end within the first hole of the shaft. In some, but not necessarily all, examples, the flex arrester(s) and the first hole(s) are sized to have a clearance fit such that the seventh material may flow by capillary action into gaps between the external surface of the flex arrester(s) and the internal surface of the shaft. At block 2504, sub-method comprises brazing the flexi arrester(s) into the first hole(s) of the shaft. The step of brazing comprises providing the seventh material. The seventh material is provided into gaps between the external surface of the flexible arrester(s) and the internal surface of the shaft. The step of brazing further comprises heating the fastener. In some, but not necessarily all examples, block 2504 comprises vacuum furnace brazing. In other examples, block 2504 comprises continuous process brazing. Alternatively, other known methods of brazing may be used. In some, but not necessarily all, examples, block 2504 is followed by block 2506. At block 2506, sub-method 2500 comprises heat treating the fastener. There is therefore provided a method 1900 comprising: providing one or more flex arresters; and attaching the one or more flex arresters to the shaft. In some, but not necessarily all, examples, method 1800 or method 1900 is followed by one or more of method 2000 (illustrated in FIG. 20A), method 2040 (illustrated in FIG. 20B), or method 2060 (illustrated in FIG. 20C). In some examples, method 2040 is an alternative to method 2000. Method 2000 comprises, at block 2002, providing one or more washer(s). Method 2000 comprises, at block 2004, providing one or more nut(s). There is therefore provided a method 2000 comprising: providing a washer; and providing a nut. Method 2040 comprises, at block 2042, providing one or more locknut(s). There is therefore provided a method 2040 comprising: providing a locknut. Method 2060 comprises, at block 2062, providing one or more sensors. There is therefore provided a method 2060 comprising: providing a sensor. FIG. 26 illustrates an example fastener 2600. The fastener 2600 comprises a shaft 2602 comprising a first material. In FIG. 26, the fastener 2600 is not shaded. The shaft 2602 comprises a first portion 2604, extending from a first end 2606 of the shaft 2602 towards a second end 2608 of the shaft 2602, opposite the first end 2606, and a second portion 2610 extending from the second end 2608 of the shaft 2602 towards the first end 2606. The first portion 2604 has a larger diameter than the second portion 2610. In some but not necessarily all examples, the first portion 2604 and second portion 2610 are separated by a third portion 2612. In some such examples, the third portion 2612 provides a chamfer between the larger diameter of the first portion 2604 and the smaller diameter of the second portion 2610. In some but not necessarily all examples, the shaft 2602 has a circular cross-section. In some but not necessarily all examples, the shaft 2602 has a constant or substantially constant cross-section. In some but not necessarily all examples, the shaft 2602 has a constant cross-section, that is, no hole (such as the first and third holes described above) extends through the shaft. The fastener 2600 comprises a sleeve 2614 comprising a second material. In FIG. 26, the sleeve is illustrated using diagonal line shading. The sleeve 2614 comprises an externally threaded portion 2616. In the example of FIG 26, the externally threaded portion 2616 extends the whole length of the sleeve 2614. In other examples, the externally threaded portion 2616 extends less than the whole length of the sleeve 2614. The sleeve 2614 comprises a hole 2618. The hole 2618 extends along a central elongate axis B of the sleeve 2614 from a first end 2620 of the sleeve 2614 to a second end 2622 of the sleeve 2614, opposite the first end. The hole is therefore a central hole. In some but not necessarily all examples, the sleeve 2614 and the hole 2618 have a circular cross-section. The hole 2618 has a constant or substantially constant crosssection such that the sleeve 2614 has a constant or substantially constant cross section. The hole 2618 is sized to receive the second portion 2616 of the shaft 2602. In some but not necessarily all examples, the sleeve 2614 has the same or substantially the same external diameter as the first portion of the shaft 2602. In some, but not necessarily all examples, the sleeve is sized to entirely cover the second portion of the shaft. In some such examples, the sleeve is sized to additionally (partly or entirely) cover the third portion of the shaft. In other examples, the sleeve is sized to cover some, but not all, of the second portion of the shaft. An external surface of the shaft 2602 is attached to an internal surface of the sleeve 2614, defined by the hole 2618, by a third material 2624 having a lower melting point than the first material and the second material. In FIG. 26, the third material 2624 is illustrated using solid black shading. In some, but not necessarily all examples, the second portion 2616 of the shaft 2602 and the hole 2618 of the sleeve 2614 are sized to have a clearance fit or an interference fit such that the third material 2624 may flow by capillary action into gaps between the external surface of the sleeve 2614 and the internal surface of the shaft 2602. An interference fit enables flowing of the third material when the fastener 2600 is heated during brazing. This provides for full gap fill coverage by the third material 2624. FIGs 27 - 28 illustrate examples of a method 2700 and sub-method 2800. Method 2700 is a method of manufacturing a fastener, such as fastener 2600. Method 2700 comprises, at block 2702, providing a shaft. The shaft comprises a first material. The shaft comprises a first portion, extending from a first end of the shaft towards a second end of the shaft, opposite the first end, and a second portion extending towards a second end of the shaft. The first portion has a smaller diameter than the second portion. In some, but not necessarily all examples, the first portion and the second portion are separated by a third portion. In some such examples, the third portion provides a chamfer between the larger diameter of the second portion 2616 and the smaller diameter of the first portion. In some, but not necessarily all, examples, block comprises producing the first, second and, optionally, the third portions. In some but not necessarily all examples, block comprises taking a blank with a first diameter and decreasing the diameter of an end portion to a second diameter, to produce the first portion with the first diameter and the second portion with the second diameter, smaller than the first diameter. In some but not necessarily all examples, block further comprises providing a chamfer between the larger first portion and the smaller second portion to produce the third portion. Method 2700 comprises, at block 2704, providing the sleeve. In some, but not necessarily all, examples, block 2704 comprises producing the sleeve. The sleeve comprises a second material. The sleeve comprises a hole extending along a central elongate axis of the sleeve from a first end of the sleeve to a second end of the sleeve, opposite the first end. Method 2700 comprises, at block 2706, attaching the sleeve to the second portion of the shaft. In some, but not necessarily all, examples, block 2706 comprises sub-method 2800, as illustrated in FIG 28. At block 2082, the method comprises copper plating the shaft and / or the sleeve. At block 2804, the method 2800 comprises positioning the second portion of the shaft within the hole of the sleeve. In some, but not necessarily all, examples, the hole is sized to receive the second portion of the shaft. In some, but not necessarily all, examples, an external diameter of the sleeve is the same or substantially the same as the second diameter. In some, but not necessarily all, examples, the second portion of the shaft and the hole of the sleeve are sized to have a clearance fit or an interference fit such that the third material may flow by capillary action into gaps between the external surface of the shaft and the internal surface of the sleeve. An interference fit enables flowing of the third material when the fastener is heated during brazing. This provides for full gap fill coverage by the third material. At block 2806, the sub-method 2800 comprises brazing the second portion of the shaft into the hole of the sleeve. In some but not necessarily all examples, the step of brazing comprises providing the third material. The third material is provided into gaps between the external surface of the shaft and the internal surface of the sleeve. The step of brazing further comprises heating the fastener. In some but not necessarily all examples, sub-block 2804 comprises vacuum furnace brazing. In other examples, sub-block 2804 comprises continuous process brazing. Alternatively, other known methods of brazing may be used. In some but not necessarily all examples, block 2804 is followed by block 2806. At block 2808, the method comprises heat treating the fastener. Returning to FIG 27, at block 2708, the method comprises producing an external thread on the sleeve. In some but not necessarily all examples, producing the external thread comprises rolling the external thread. There is therefore provided a method of manufacturing a fastener comprising: providing a shaft; providing a sleeve; attaching the sleeve to the shaft; and heat treating the fastener. In some examples, the blocks of the method are carried out in the order indicated above. In other examples, the blocks of the method may be carried out in a different order. For example: Block 2708 may be carried out before block 2706; that is, the external thread on the sleeve may be produced before the sleeve is attached to the shaft. Block 2708 may be carried out after block 2804 and before block 2806; that is, the external thread on the sleeve may be produced after the sleeve is attached to the shaft by brazing, but before heat treatment of the fastener. Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described. The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to ‘comprising only one...’ or by using ‘consisting.’ In this description, the wording ‘connect’, ‘couple’ and ‘communication’ and their derivatives mean operationally connected / coupled / in communication. It should be appreciated that any number or combination of intervening components can exist (including no intervening components), i.e., to provide direct or indirect connection / coupling / communication. Any such intervening components can include hardware and / or software components. In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’, or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example. Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims. Features described in the preceding description may be used in combinations other than the combinations explicitly described above. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. The description of a feature, such as an apparatus or a component of an apparatus, configured to perform a function, or for performing a function, should additionally be considered to also disclose a method of performing that function. For example, description of an apparatus configured to perform one or more actions, or for performing one or more actions, should additionally be considered to disclose a method of performing those one or more actions with or without the apparatus. Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not. The term ‘a’, ‘an’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a / an / the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’, ‘an’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning. The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result. In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described. The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description. Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure. 5 Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not emphasis has been placed thereon. 10 l / we claim:

Claims

1. A fastener comprising:a shaft, comprising a first material, the shaft comprising a first hole extending5 along a central elongate axis of the shaft from a first end of the shaft towards a second end of the shaft, opposite the first end; anda pipe, comprising a second material, the pipe comprising a second hole extending along the central elongate axis of the shaft from the first end of the pipe to a second end of the pipe, and provided within the first hole of the shaft, where an10 external surface of the pipe is attached to an internal surface of the shaft, defined by the first hole, by a third material having a lower melting point than the first material and the second material.

2. A fastener as claimed in claim 1, wherein the second material has different15 material characteristics to the first material.

3. A fastener as claimed in any preceding claim, wherein the external surface of the pipe is attached to the internal surface of the shaft by brazing, and wherein the third material is a filler material.

204. A fastener as claimed in any preceding claim, wherein the shaft comprises: a first externally threaded portion, extending from the first end of the shaft along at least a portion of the shaft.25 5. A fastener as claimed in claim 4, wherein the shaft comprises a secondexternally threaded portion, extending along the central elongate axis of the shaft from the second end of the shaft towards the first end of the shaft.

6. A fastener as claimed in claim 4, wherein the first externally threaded portion 30 is formed by rolling.

7. A fastener as claimed in any preceding claim, wherein an end of the first hole, opposite the first end, is rounded, and / or an end of the second hole, opposite the second end, is rounded.07 02 258. A fastener as claimed in any preceding claim, comprising a first insert, positioned within the second hole of the pipe.5 9. A fastener as claimed in claim 8, wherein the insert provides a closed end ofthe pipe.

10. A fastener as claimed in claim 8 or 9, wherein:the second hole of the pipe has a rounded end; and10 the insert has a rounded end, shaped to fit within the rounded end of the second hole.

11. A fastener as claimed in any of claims 8-10, wherein an external surface of the insert is attached to an internal surface of the pipe, defined by the second hole, 15 by brazing.

12. A fastener as claimed in any preceding claim, comprising a spherical washer.

13. A fastener as claimed in any preceding claim, comprising one or more20 sensors, positioned within the shaft or the pipe, the one or more sensors configured to detect at least one of: a flaw in the shaft and / or the pipe; or a change in the material properties of the shaft and / or the pipe.

14. A fastener as claimed in any preceding claim, comprising a head provided at 25 the second end of the shaft.

15. A fastener as claimed in claim 14, wherein the head is one of: a bolt head; a substantially spherical portion; or a hex head.30 16. A fastener as claimed in any preceding claim, wherein the first hole extendsfrom the first end of the shaft to the second end of the shaft.

17. A fastener as claimed in any of claims 14-16, comprising a third insert, provided within the first hole, wherein a cross-sectional area of the third insert07 02 25decreases from an outer end, positioned on the head of the shaft, to an inner end, positioned within the first hole.

18. A fastener as claimed in any of claims 1-13, wherein the shaft comprises a 5 third hole extending along the central elongate axis of the shaft from the second end of the shaft towards the first end of the shaft, the third hole extending along at least a portion of the shaft to form a second hollow portion of the shaft.

19. A fastener as claimed in claim 18, wherein a first hollow portion of the shaft, 10 through which the first hole extends, and the second hollow portion of the shaft are separated by a solid portion.

20. A fastener as claimed in claim 18 or claim 19, comprising a second pipe, comprising the second material, the second pipe comprising a fourth hole extending 15 along a central elongate axis of the second pipe from a first end of the second pipe to a second end of the second pipe, and provided within the third hole of the shaft, wherein an external surface of the second pipe is attached to an internal surface of the shaft, defined by the third hole, by the third material.20 21. A fastener as claimed in claim 20, comprising a second insert, positionedwithin the fourth hole of the pipe.

22. A fastener safety detection system, comprising:a fastener as claimed in any of claims 13-21; and25 means for providing an alert in response to a detection of at least one of: a flaw in the shaft and / or the pipe; or a change in the material properties of the shaft and / or the pipe.

23. A method of manufacturing a fastener, comprising:30 providing a shaft, comprising a first material, the shaft comprising a first hole extending along a central elongate axis of the shaft from a first end of the shaft towards a second end of the shaft, opposite the first end;providing a pipe, comprising a second material, comprising a second hole extending along the central elongate axis of the pipe from the first end of the pipe to the second end of the pipe, wherein providing the pipe comprises extruding the pipe;providing the pipe within the first hole of the shaft; and5 attaching an external surface of the pipe to an internal surface of the shaft, defined by the first hole, using brazing, such that the external surface of the pipe is attached to the internal surface of the shaft by a third material having a lower melting point than the first material and the second material.10 24. A method as claimed in claim 23, wherein the direct product of the method isa fastener.

25. A method as clamed in claim 24, wherein the fastener is a fastener asLDCMclaimed in any of claims 1 - 21.15CM

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