Locked coupling with setpoint clamping torque

Abstract

The invention relates to a coupling (100) for connecting two pipes (C1, C2), comprising: - a first end piece (1) suitable for a first pipe (C1) and having a threaded segment at its free end, - a second end piece (2) suitable for a second pipe (C2) and intended to be clamped against the first end piece (1), - an internally threaded clamping nut (3) carried by the second end piece (2) and clamping the latter against the first end piece (1), - the nut (3) being screwed onto the threaded segment of the first end piece (1), and also comprising a member (4) for locking the nut (3) in a setpoint clamping position of the coupling (100), the locking member (4) comprising an in particular elastic tab (424) received, in the setpoint clamping position, in a cavity of the end piece (1).

Description

[0001] Title: Torque setting fitting locked

[0002] The present invention relates to a locking, set torque fitting.

[0003] There are many types of pipe fittings, generally consisting of two ends associated respectively with the two pipes to be connected and a nut carried by one of the ends and sliding onto the other.

[0004] When tightening such a fitting, care must be taken to avoid crushing the sealing elements between the two ends, ensuring a proper seal. Furthermore, this tightness, once achieved, can loosen for various reasons, including vibrations or fluid shocks within the pipes.

[0005] The present invention aims to develop a torque-set fitting that can be locked in this tightening position in a simple, easily accessible manner and that can nevertheless be opened.

[0006] To this end, the invention, according to a first aspect, relates to a torque-controlled fitting for connecting two pipes comprising: a first fitting fixed to a first pipe, and having on its free side a threaded segment ending in an end forming a sealing surface, a second fitting fixed to a second pipe, and having an end with a sealing collar provided with a lip intended to be tightened against the sealing surface of the first fitting, a tightening nut carried by the second fitting and tightening it against the first fitting, the nut fitted, free to rotate on the second fitting, overlapping its sealing collar and screwing onto the threaded segment of the first fitting to push against the collar and tighten the sealing lip against the sealing surface, the first fitting having a nut ring to hold the fitting for screwing,The set tightening torque of the fitting corresponds to the optimal elastic deformation of the sealing lip; this fitting is characterized by a locking device for the nut in the set tightening position of the fitting.

[0007] This fitting has the advantage of allowing the set tightening position to be defined in advance, in order to obtain the sealing of the fitting under the best conditions of reliability of the elements making the seal such as the sealing collar of one of the ends and the sealing surface of the other, by a very simple installation of a locking element of the nut which, nevertheless can be detached to allow, if necessary, to open the fitting.

[0008] In this fitting, the thread of the first end receiving the clamping nut is extended beyond the set clamping position so that this set clamping position precedes the end position of screwing the nut onto the end, which has the advantage of allowing the set clamping position to be fixed without imposing a precise length of the thread of the first end receiving the nut.

[0009] According to another advantageous feature, the locking member is a ring assembled rotationally to the inner side of the nut, beyond its threaded segment and formed of a band equipped with at least one lock consisting of a strip cut from the band to which it remains attached by one end, its other end forming a locking lug projecting outwards from the ring and ending in a tab projecting inwards from the ring,

[0010] - the lug being pushed elastically into protrusion by the lamella,

[0011] - the ring being housed in a groove of the sleeve extending axially from the nut beyond its threaded hole,

[0012] - the lug being engaged by the push of the tongue in a transverse passage of the sleeve and held in this passage in rotation with the nut,

[0013] - the end piece having a smooth crown on which the ring and the locking lug rest, at least towards the end of the nut being screwed onto the end piece,

[0014] - the smooth ring having at least one cavity defining the locking position of the setpoint clamping on the peripheral path of the lug driven by the screwing movement of the nut to receive the lug of the locking member and to block in this position the rotation of the nut relative to the end piece.

[0015] This locking element and the locking means carried by the two tips constitute simple manufacturing methods, not modifying the characteristics of the tips while allowing a quick and guaranteed installation of the clamping locking element.

[0016] According to another advantageous feature, the free end of the tongue is folded back on itself to form the lug, oriented radially and extending under the tongue to form the radially protruding leg.

[0017] According to another advantageous feature, the ring has three locks distributed equiangularly on the ring which allows the most accessible lock to be chosen for the installation of the locking device in an environment which is often complicated and difficult to access.

[0018] According to another advantageous feature, the ring is an open ring with a cut and formed by a ribbon in which the tabs are cut leaving cutting windows, the ribbon is then bent and the tab is shaped into a lug by bending the ribbon into a ring whose ends of the ribbon are left free to form the cut, which constitutes a ring that is particularly simple to make and install on the nut.

[0019] According to another advantageous feature, the crown has an annular relief in which one or more cavities are made depending on the locks, the annular relief having a diameter close to that of the top of the threaded segment of the first end, which allows the continuity of screwing the nut and also that of unscrewing for an intervention on the fitting.

[0020] According to another advantageous characteristic,

[0021] - the end piece receiving the nut has at least one blind hole on its periphery, beyond the threaded segment and before the nut ring, and

[0022] - the locking nut consists of a stud whose head is fitted with a ring to engage it in the blind hole through a passage in the peripheral direction, associated with the blind hole of the setpoint tightening,

[0023] - an elastic rider shaped to carry the stud to clip onto the nut sleeve and hold the stud in the blind hole.

[0024] According to another advantageous feature, the fitting has three locking points with a respective blind hole, these blind holes being distributed equiangularly and corresponding to the same set tightening force, the stud being intended to be engaged in the most accessible blind hole through the passage associated with this blind hole.

[0025] According to another advantageous feature, the first end piece has a blind hole defining the set tightening position and the nut has a locking element in the form of a spring stud, carried by the end of the nut and coming into the blind hole when the nut is screwed into the set tightening position.

[0026] According to another favorable aspect of the invention, independent of the first aspect but which can be favorably combined with it, a fitting according to claim 1 is envisaged, with improvements and favorable embodiments being defined in the subclaims. The present invention will be described in more detail below with reference to embodiments of a fitting, shown in the accompanying drawings in which:

[0027] [Fig. 1] Perspective view in axial half-section of a first embodiment of the connection,

[0028] [Fig. 2] Cutaway perspective view of the nut of the fitting in Figure 1, [Fig. 3] Perspective and front views of the locking ring of the fitting,

[0029] [Fig. 4] Perspective view in half-axial section of the nut of the fitting in figure 1,

[0030] [Fig. 5] Perspective view in axial half-section of the fitting tip of figure 1,

[0031] [Fig. 6A] Cross-sectional view of the fitting by a cutting plane perpendicular to the axis of the fitting,

[0032] [Fig. 6B] View of the fitting in the first stage of screwing,

[0033] [Fig. 6C] View of the fitting in a second screwing stage,

[0034] [Fig. 6D] Axial cross-sectional view of the fitting in Figure 6A in the locked position,

[0035] [Fig. 6E] Axial cross-sectional view of the fitting in Figure 1 in the initial unlocking position,

[0036] [Fig. 7A] Enlarged detailed view of a fitting locking point with the nut slightly upstream of the locking position, [Fig. 7B] Enlarged detailed view of a fitting locking point with the nut in the locking position,

[0037] [Fig. 8] Perspective view in axial half-section of a second embodiment of the connection,

[0038] [Fig. 9A] Cross-sectional view perpendicular to the axis, of the fitting and its locking mechanism,

[0039] [Fig. 9B] Cross-sectional view through the plane of symmetry of the locking mechanism of the fitting in figure 9A,

[0040] [Fig. 10] Exploded view in axial half-section of a third embodiment of the fitting,

[0041] [Fig. 11] Axial cross-sectional view of the fitting of the third embodiment of the fitting in the assembled state.

[0042] [Fig. 12] Detailed view of the spring stud of the fitting in Figure 11.

[0043] Figure 1 shows a first embodiment of a fitting 100 with a set tightening torque for connecting two simply sketched pipes C1, C2. The fitting 100 consists, along the axis XX, of a first end fitting 1 fixed to the first pipe C1 and a second end fitting 2 fixed to the second pipe C2, as well as a clamping nut 3 carried by the second end fitting 2 and tightening it against the first end fitting 1. The second end fitting 2 has one end fitted with a sealing collar 21 with a lip 211 for tightening against the sealing surface 13 of the first end fitting 1.

[0044] Nut 3 is fitted, free to rotate, onto the second end piece 2 by overlapping its sealing collar 21 to screw onto the threaded segment 12 of the first end piece 1 to push against the collar 21 and tighten its sealing lip 211 against the sealing surface 13 of the first end piece.

[0045] The first bit 1 has a nut ring 11 for screwing. It also has an angular marker in the form of a mark l ia, for example a line on a facet 111 of its nut ring 11.

[0046] By definition, the first end 1 is the fixed part of the fitting and the element 3, which is the nut, is screwed onto the first end 1. The direction of screwing is clockwise.

[0047] More specifically, according to Figure 2, the nut 3 has a faceted nut head 31, for example, a hexagonal nut. One facet has a mark 31a associated with the mark 1a of the first fitting 1 to identify, if necessary, the set tightening position; the start and pitch of the thread of the threaded segment 12 of the first fitting 1 and the start and pitch of the tapped segment 33 of the nut 3 are designed so that the positioning of the nut 3 at the end of tightening onto the first fitting 1 corresponds approximately, preferably, but not necessarily, to the set tightening of the fitting 100 with the optimal elastic deformation of the sealing lip 211. For various reasons, the set tightening position is not the end-of-tightening position of the nut 3 on the fitting 1.

[0048] A locking member 4 is associated with the nut 3 to lock it relative to the first end piece 1 when the nut 3 is in its set screw position on the end piece 1. The locking member 4 consists in this example of a ring 41 fixed in rotation to the nut 3 and locking to the end piece 1 in the predefined position corresponding to the set tightening.

[0049] To simplify the description, the tightening direction (V) of nut 3, which is always clockwise, is indicated in the figures according to the observer's position (or the figure's orientation). By convention, the front side AV of fitting 100 is the half-space occupied by the first end piece 1 relative to an unshown plane perpendicular to the axis XX of fitting 100; the rear side AR is that of the other half-space. Figure 3 shows, in parts A and B, a front view and a perspective view of ring 41 from the front side AV, so that the tightening direction (S) of nut 3 and the ring 41 it carries appears to be counterclockwise. The tightening direction V is the same as in Figures 1 and 2, showing nut 3 located on the rear side of the fitting and therefore tightened clockwise from the rear side of the fitting.The rotation position shown should be considered as any angular orientation position around the XX axis.

[0050] The ring 41 is formed by a band of a resistant elastic material such as, for example, a band of spring steel or stainless steel cut and shaped with locks 42 to be rotationally fixed to the nut 3.

[0051] The locks 42 each consist of a tab 421 cut lengthwise from the ribbon and remaining attached to it by its end 421a; the tab 421, forming a leaf spring, terminates in its cutout window 422 with a folded end forming a locking lug 423 projecting outwards from the ring. This locking lug 423 extends into a tab 424 projecting inwards from the ring.

[0052] The ring 41 is an open ring with a cut 43 to allow its elastic deformation as will be seen later. This cut 43 consists, at the respective end of the ring 41, of a straight edge 431, facing a folded edge 432 in the form of a step to constitute both a stop against compression of the ring and a support for the straight edge 431 on and in the step thus formed.

[0053] Figures 4 and 5, shown side by side, are perspective views, axial section of the clamping nut 3 and the first end piece 1, highlighting the shape of the end piece 1 with its smooth ring 14 between the threaded segment 12 and the nut ring 11.

[0054] According to figure 4, the inside of the nut 3 has a bearing surface 32 to bear against the bearing ring 212 of the second end piece 2, followed by a thread 33 and a sleeve-shaped part 34 with, the inner side of which has a groove 341 receiving the ring 41 of the locking member 4.

[0055] This cross-sectional view (Figure 4) shows half of the ring 41 delimited by the axial plane of the section. The groove 341 opens through transverse passages 342 forming locking points PVi which receive the lugs 423. The locking points PVi, in the groove 341, are in peripheral positions, distributed, homologous to those of the lugs 423 of the ring 41 in order to retain the ring 41 in the peripheral direction and allow the nut 3 to be screwed onto the end piece 2 and then locked as soon as the set tightening torque is reached, as will be described below.

[0056] In Figure 4, the screwing position (rotation position) of nut 3 corresponds to its set tightening position, as detailed in Figures 6A-6D; arrow V indicates the screwing direction of nut 3 viewed from the front side AV along axis XX. The end piece 1 is, by design, fixed relative to axis XX, and nut 3 is screwed onto it.

[0057] During the tightening of nut 3, the lugs 424 first bear against the thread 12 of the tip 1 and then progressively against the annular relief

[0058] 140 of the smooth groove 14 forming a ring of equal or near-equal height to that of the thread edge 12, the bottom of the ring 14 being level with the bottom of the thread. The lugs 424 bear against the annular relief 140 until the nut 3 reaches the specified tightening position relative to the end piece 1; this position corresponds to the cavity 141 of the locking point PVi of the groove 14 for each locking point. The cavity 141 is formed in the annular relief 140.

[0059] This cavity 141 is positioned angularly and longitudinally with respect to the axis XX; this means that the angular position alone is not sufficient for the leg 424 to engage radially in the cavity

[0060] 141; it is also necessary that the lug 424 not be partially (in the direction of the axis XX) straddling the cavity 141, but be longitudinally positioned exactly on the cavity 141 along the direction of the axis XX. The cavity 141 is positioned longitudinally according to the thread pitch of the thread 12.

[0061] Reference mark 31a allows one to find by sight the concordance, at least approximate, between reference mark 31a and mark l ia indicating to the operator that nut 3 is approaching the set tightening position.

[0062] The diagrams in Figures 6A, 6B, 6C, and 6D show the tightening steps of nut 3 onto end piece 1. These figures are schematic cross-sectional views (from the front AV) so that the clockwise tightening direction V is represented in reverse. They are limited to the schematic representation of nut 3 by its nut ring 31 and the sleeve 34 with the groove 341 housing the ring 41 and its locking tabs 42 engaging in the passages 342. The ring 41 is held against the bottom of the groove 341 and the lugs 423 are engaged in the passages 342.

[0063] The fitting 100 has three locks 42 distributed at 120° on the ring 41; the groove 341 of the sleeve 34 has three passages 342 corresponding to the position of the three lugs 423 on the ring 41 and therefore of the locks 42.

[0064] The annular relief 140 of the smooth crown 14, has its cavities 141 at the positions of the blocking points PVi (PV1, PV2, PV3).

[0065] The 141 / PVI cavity of the tip 1 is located, as an example, on the ZZ axis and the other two cavities are at 120°.

[0066] Figure 6A shows a position of the nut 3 in its approach phase to the locking position of the set tightening from this angular position ( 2) relative to the locking point PVI (passage 141) of the fixed end 1 in rotation.

[0067] Nut 3 rotates in the direction (V) and approaches the locking position (PVI) (fig. 6B) until it reaches the edge 141a of cavity 141.

[0068] Figure 6C shows the arrival of the lug 424 (as well as the two other lugs) of the lug in the cavity 141. The lug 424 is near the upstream side 141a of the cavity 141. The screwing of the nut 3 can continue for a few angular degrees until the lug 424 meets the downstream side 141b of the cavity 141, which blocks the rotation of the nut 3 (Figure 6D).

[0069] In this locking position (figure 6D), the lugs 424 are against the stop, which is transmitted to the tabs 421 locking the ring 41 which itself locks the nut 3.

[0070] It should be noted that, in all tightening and loosening positions, the lug 423 slides radially within the passage 342 without coming out of it. It may protrude radially outwards depending on the thickness of the sleeve 34 and the radial length of the lug 423 (or all the lugs 423).

[0071] The fact that the passages 342 open from the sleeve 34 allows visual control of the positioning of the ring 41 in the groove 341. This also facilitates the creation of these passages by machining from the outside.

[0072] However, if necessary, the passages 342 could be limited to a non-opening transverse cavity. In all cases, the passage 342 is transverse, that is to say, oriented longitudinally along the axis XX in such a way as to accommodate the folding of the slat 421, the end of which forms the lug 423, which has a radial and longitudinal orientation.

[0073] Figure 6E shows the possible unscrewing maneuver. To do this, the nut 3 is rotated in the counterclockwise direction (DV), which is a pulling movement exerted on the lug 424. The lug rises under the action of the rotation and the slope of the lug 424.

[0074] Figures 7A, 7B show, on an enlarged scale, the engagement of leg 424 in cavity 141 of a locking point PVi.

[0075] Figure 7A shows a screwing position of the nut 3 upstream of the setpoint tightening position. The lug 423 is engaged in the transverse passage 342 of the nut, lifted by the tab 424 bearing against the annular relief 140 of the groove 14 through the cutout 422 of the ring 41 against the thrust exerted by the tab 421 carrying the lug 423. The latter is fully engaged in the passage 342.

[0076] Having reached the entrance of cavity 141 by the continued rotation of nut 3, the tab 424 is pushed into cavity 141 against the upstream side 141a (Figure 7B) by the tab 421 acting as a return spring. Nut 3 can continue to pivot ring 41 a few degrees until it locks against the downstream side 141b of cavity 141.

[0077] Figures 8, 9A, 9B show another embodiment of a fitting 100a equipped with a locking device 4a for the fitting in the set tightening position.

[0078] This fitting 100a, like the previous fitting 100, is designed to join two pipes connected respectively to a first fitting 1 and a second fitting 2. The first fitting 1 has a thread 12 and a bearing surface 13, and the second fitting 2 terminates with a sealing collar 21 with a sealing lip 211 and a support ring 212. The nut 3a, which rotates freely on the second fitting 2, screws onto the thread 12 of the first fitting 1 to tighten the end of the second fitting 2 and assemble the fitting. The screw is locked at the set tightening position by a locking member 4a with a stud 41a carried by a bracket 411a. The first fitting 1 has blind holes 151 distributed around its periphery, for example, three blind holes spaced 120° apart, which can serve as reference points for the set tightening position.The nut 3a, whose periphery overlaps the crown of the end piece 1 beyond its thread on which it screws, has a peripheral passage 342a in the form of an oblong hole which covers the blind hole 151 of the end piece 1 when the nut is in its screwed position at the set tightening.

[0079] The locking member 4a consists of a stud 41a whose head is fitted with a ring 411a to engage it in the blind hole 151 of the end piece 1.

[0080] The length of the oblong hole forming the passage 342a in the peripheral direction is reduced to just compensate for the imprecision of screwing the nut 3a with the blind hole 151 around the locking point PVi / PVl.

[0081] The locking member 4a is completed by a saddle 42a shaped like a bracket carrying the stud 41a. The elastic saddle 42a has an arched shape with a length greater than half the perimeter of the sleeve 34a of the nut 3a in order to clip onto it and hold the stud 41a in the blind hole 151. The two ends 421a of the saddle 42a are rounded, for example, in a loop to facilitate its clipping onto the sleeve 34a of the nut and to slide on its wall both when clipping and unclipping if the stud 41a needs to be removed.

[0082] In this embodiment, the fitting 100a has three locking points PV1, PV2, PV3 with a respective blind hole 151 and the nut 3a has three peripheral oblong holes 342a, associated with the locking points PV1, PV2, PV3 distributed equiangularly around the periphery and corresponding to the same set tightening force so that on this periphery, at least one of the locking points PVi is easily accessible if the pipes and the fitting 100a are in a congested environment.

[0083] Thus, when the nut 3a is tightened in the set position, its oblong holes 342a on the periphery each overlap a blind hole 51 of the first end piece 1 and allow the locking member 4a, whose head is connected to a ring, to engage in the most accessible locking point PVi; this locking of the nut 3a is sufficient.

[0084] This locking element 4a is easily removed from the fitting 100a by a simple pull exerted on the ring 411a.

[0085] Figures 10 to 12 show another embodiment of a 100b fitting with a locking nut. As before, this fitting consists of a first end 1 connected to a first pipe and a second end 2 connected to a second pipe. The two ends 1 and 2 are clamped together by a nut 3b, which rotates freely on the second end 2 and bears with its bearing surface 32b against the sealing flange 21 of the second end 2, pushing it against the sealing surface 13 of the first end 1. In this assembled position, the nut 3b is screwed onto the thread 12 of the end of the first end 1 until the seal formed by the lip 211 of the end of the second end 2 is clamped against the sealing surface 13 of the first end 1, according to the set tightening torque.

[0086] In the set tightening position, the spring stud 4b carried by the end of the nut 3b comes into a blind hole 151 positioned appropriately at the periphery of the first end piece 1 in the set tightening position.

[0087] The tapping of the nut 3b and the thread 12 of the first end piece 1 are machined so that the set tightening position corresponds to the coincidence of the locking member 4b carried by the nut 3b and the blind hole 151 of the first end piece 1.

[0088] NOMENCLATURE OF MAIN ELEMENTS (without alphabetical suffixes unless necessary)

[0089] 100 Fitting

[0090] 1 First nozzle

[0091] 11 Crown nut l ia Brand

[0092] 111 Facet

[0093] 12 Threaded segment

[0094] 13 Sealing surface

[0095] 14 Smooth crown

[0096] 140 Ring relief

[0097] 141 Transverse cavity

[0098] 141a Upstream side

[0099] 141b Downstream side

[0100] 151 Blind hole

[0101] 2 Second nozzle

[0102] 21 Sealing collar

[0103] 211 Sealing lip

[0104] 212 Supporting crown

[0105] 3. Clamping nut

[0106] 31 Nut head

[0107] 31a Reference

[0108] 311 Tool grip facet

[0109] 32 Supporting surface

[0110] 33 Tapping

[0111] 34 Sleeve

[0112] 341 Gorge

[0113] 342 Transverse passage

[0114] 342a Peripheral passage

[0115] 4. Locking mechanism

[0116] 4a Ring stud

[0117] 4b Spring stud

[0118] 41 Open ring

[0119] 41a Goujon

[0120] 411a Ring

[0121] 42 Lock

[0122] 42a Elastic rider

[0123] 421 Tongue

[0124] 421a Rider's End

[0125] 422 Cutting window

[0126] 423 Locking lug in the shape of a folded end

[0127] 424 Leg facing inwards towards the ring

[0128] 43 Ring Cut

[0129] 431 Transverse end 432 Step

[0130] XX Connection axis Cl Pipe C2 Pipe V Tightening direction DV Loosening direction PVi Locking point

Claims

DEMANDS 1. Fitting (100) for connecting two pipes (Cl, C2) comprising: - a first end piece (1) adapted to a first pipe (Cl), and having on its free side a threaded segment (12), - a second nozzle (2) adapted to a second pipe (C2), intended to be tightened against the first nozzle (1), - a threaded clamping nut (3) carried by the second end piece (2) and clamping it against the first end piece (1), - the nut (3) screwing onto the threaded segment (12) of the first end (1), characterized in that it is provided with a locking element (4) for the nut (3) in a set tightening position of the fitting (100), the locking element (4) comprising a tab (424), in particular elastic, received, in the set tightening position, in a cavity (141) of the end (1).

2. Fitting (100) according to claim 1, characterized in that the cavity (141) is formed on an external lateral face of the nozzle (1).

3. Fitting (100) according to claim 1 or 2, characterized in that the lug (424) protrudes from the inner lateral face of the nut (3).

4. Fitting (100) according to any one of claims 1 to 3, characterized in that the locking member (4) comprises a ring (41) rotationally fixed to the inner side of the nut (3) and formed of a band having at least one lock (42) consisting of a tab (421) cut out of the band to which it remains attached by one end (421a), its other end forming a locking lug (423) projecting outwards from the ring and terminated by the tab (424) projecting inwards from the ring (41), the lug (423) being elastically pushed outwards by the tab (421), the ring (41) being housed in a groove (341) of the nut (3), preferably beyond its thread (33), - the lug (423) being engaged by the push of the tongue in a hole, for example a transverse passage (342), of the sleeve (34), and held in this passage securely in rotation of the nut (3).

5. Fitting according to any one of the preceding claims, characterized in that - the tip (1) has a crown (14) on which the lug (424) of the lock (42) rests at least towards the end of the screwing of the nut (3) onto the tip (1), - the crown (14) having at least one cavity (141) defining the locking position (PVi) of the setpoint tightening.

6. Fitting (100) according to claim 4 or 5, characterized in that the free end of the tongue (421) is folded back on itself to form the lug (423), oriented radially and extending under the tongue (421) to form the radially projecting tab (424).

7. Fitting (100) according to any one of claims 4 to 6, characterized in that the ring (41) is an open ring with a cut (43) and formed by a ribbon in which the tabs (421) are cut leaving cutting windows (422), the ribbon being then bent and the tab formed into a lug (423) by bending the ribbon into a ring (41) whose ends (431, 432) of the ribbon are left free to form the cut (43).

8. Fitting (100) according to claim 3 and one of claims 5 to 7, characterized in that the crown (14) has an annular relief (140) in which the one or more cavities (141) are made according to the number of locks (42) of the ring (41), the annular relief (140) having a diameter close to that of the top of the threaded segment (12) of the first end piece (1).

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