Letterplate with flap restrictor

Abstract

A letterplate assembly 100 with an interior flap 103, a body 101, a side plate 201 and a pin 115. Post can be passed through a channel 109. The interior flap is mounted on an upper edge and pivots to

Description

This invention relates to letterplate assemblies. More particularly, but not exclusively, this invention relates to a letterplate assembly comprising a flap having a restricted opening angle. This invention also relates to a method of assembling a letterplate assembly comprising a flap having a restricted opening angle. A typical letterplate assembly generally includes an interior flap and an exterior flap which are pivotally mounted to respective ends of a body that provides a channel through which items of post can be passed through the letterplate assembly. In use, the body is mounted within a door, wall, or other structure of a building, for example, and the interior and exterior flaps cover over respective ends of the channel. Items of post can then be posted from the exterior side of the letterplate assembly to the interior side by lifting the exterior flap and pushing the items through the channel. A problem associated with known letterplate assemblies is that they can provide relatively easy access to the interior of a building for burglars. For example, someone located on a building’s exterior may be able to insert a tool through the channel of the letterplate assembly in order to retrieve items such as keys located within the building. This sort of attack is sometimes referred to as a fishing attack. Alternatively or additionally, someone may be able to manipulate parts of the door lock located on the interior side of the door, such as a thumb turn, via the letterplate assembly in order to gain access to the building. Another potential security flaw associated with known letterplate assemblies is that someone may also be able to look through the channel into the building to assess whether the building is occupied or whether items suitable for fishing are located within reach. To mitigate against the above-mentioned attacks, known letterplate assemblies can be provided with a flap which cannot be opened beyond a specified restricted opening angle. In some cases, the opening angle of the flap must be restricted after the letterplate assembly has been installed. As such, the means of restricting the flap must be configured by the person installing the letterplate assembly. It is therefore desirable to provide an easy and reliable way of restricting the flap during the process of assembling the letterplate assembly. The present invention seeks to provide an improved letterplate assembly and an improved method of installing a letterplate assembly. Alternatively or additionally, the present invention seeks to provide a letterplate assembly that mitigates one or more of the above mentioned disadvantages associated with known letterplate assemblies. Summary of the Invention The present invention provides, according to a first aspect, a letterplate assembly comprising a first flap, a body, a first side plate, and a first restricting member. The body comprises a channel through which post can be passed from a first side of the letterplate assembly to a second side of the letterplate assembly. The first flap is pivotally mounted to the body at the second side of the letterplate assembly, the first flap being pivotally mounted at or near an upper edge of the first flap, the first flap being pivotable between an open position and a closed position in which the first flap covers an opening of the channel. The first side plate extends from a rear of the first flap at a first lateral side of the channel, the first side plate being formed with an opening. The first restricting member comprises a head, a non-threaded portion, and a threaded portion between the head and the non-threaded portion. The first restricting member is received within the opening of the first side plate, the first flap being prevented from pivoting beyond the open position by the first restricting member abutting with a wall of the opening. The first restricting member is fastened to the body by the threaded portion being engaged with a first part of the body at a first lateral side of the first side plate and the non-threaded portion of the first restricting member is received in a second part of the body at a second lateral side of the first side plate, the second part of the body being closer to the opening of the channel than the first part of the body. The letterplate assembly according to the first aspect of the invention is configured to be installed with the first flap positioned on an interior side of the building. As such, the first flap may also be referred to as an interior flap. The term “interior” in this context should be understood to mean the side of the door, wall, or other structure into which post is received after passing through the letterplate assembly. The letterplate assembly may have a second flap pivotally mounted to the body at the first side of the letterplate assembly. The second flap may be positioned on an exterior side of the letterplate assembly, so may also be referred to as an exterior flap. The term “exterior” in this context should be understood to mean the side of the door or wall from which post is being passed through the letterplate assembly, which may in some cases may be located within a building. The term “post” should be understood to mean any article that is deliverable through the letterplate assembly. The letterplate assembly is configured to be installed in a door, wall, or other structure so, while the letterplate assembly is described below with reference to a door, it should be understood that its use is not limited to doors only. The channel may have a minimum internal height of between approximately 20 millimetres and 30 millimetres. However, in embodiments of the invention the minimum internal height of the channel may of course be larger than this. The minimum internal height of the channel may be such that the channel is configured to receive post having a predetermined maximum thickness of between approximately 20 millimetres and 30 millimetres. For example, in some embodiments the minimum internal height of the channel may be such that the channel is configured to receive post having a thickness of up to 24 millimetres, 26 millimetres, or 30 millimetres. The channel may have a uniform height along its length. In some embodiments of the invention, the height of the floor of the channel may vary to provide the channel with a varying height along its length. Alternatively or additionally, the height of the ceiling of the channel may vary to provide the channel with a varying height along its length. When installed in a door, the length direction of the channel may generally correspond to the thickness direction of the door. The channel may have a width of between 200 and 350 millimetres, and preferably between 250mm and 305mm. The width direction of the channel may be oriented perpendicularly to the height direction of the channel. The letterplate assembly may be horizontally installed such that the width direction of the channel is oriented substantially horizontally. It will be appreciated that the letterplate assembly may be installed in other orientations, for example vertically. The position of the first restricting member within opening changes as the first flap is moved between the open and closed positions due to the first side plate moving relative to the first restricting member. The first restricting member may comprise an axis. The axis of the first restricting member may be oriented substantially parallel to a width direction of the channel. In use, when the letterplate assembly is installed within a door, wall, or other structure, the first restricting member may be oriented substantially horizontally. The letterplate assembly according to the first aspect of the invention comprises a first flap having an opening angle that is restricted by the first restricting member abutting with a wall of the opening of the first side plate when the first flap is moved to its open position. Restricting the opening angle of the letterplate assembly provides protection against fishing attacks. The restricting member comprises a threaded portion between a head and a non-threaded portion; this arrangement is particularly advantageous. During a fishing attack, the attacker could try and force the first flap beyond its open position by trying to break the first restricting member away from the body of the letterplate assembly. The force needed to do this can be increased by ensuring that the restricting member is secured to the body on both lateral sides of the first side plate, as is the case with the letterplate assembly of the first aspect of the invention. However, if a fastener such as, for example, a traditional bolt is used as a restricting member, the thread of the bolt will engage with the second part of the body, as well as the first part of the body. If the bolt is overtightened, the bolt may pull the first part of the body and the second part of the body towards one another, and potentially into contact with the first side plate. In this situation, the first side plate would be compressed between the first part of the body and the second part of the body, which would interfere with the first flap being freely opened and closed. By providing a restricting member having a non-threaded portion which engages with the second part of the body this situation is avoided because overtightening of the first restricting member simply pushes the unthreaded part of the first restricting member further into the second part of the body. The head of the first restricting member may abut the first part of the body. This arrangement may help ensure that the first restricting member is correctly installed when assembling the letterplate assembly because the first restricting member simply needs to be screwed into the first part of the body until the head abuts with the first part of the body. The body may comprise a faceplate portion, or plate portion, which defines the opening of the channel. The first part of the body may comprise a raised portion which projects from a surface of the faceplate portion at the first lateral side of the channel. The threaded portion may be engaged with the raised portion. The first flap may cover the raised portion and the restricting member, including the head of the restricting member, when in the closed position. In this arrangement, the raised portion and restricting member are hidden from view when the first flap is in its closed position, thereby providing the interior side of the letterplate assembly with an aesthetically pleasing appearance. The second part of the body into which the non-threaded portion is received may be provided by a second raised portion which projects from a surface of the faceplate portion. The second raised portion may be integrally formed with the faceplate portion. The second raised portion may be formed by a wall which extends away from the faceplate portion. The non-threaded portion may be received into an opening. The internal diameter of the opening may be approximately equal to an external diameter or cross-sectional dimension of the non-threaded portion to ensure that the first restricting member cannot be substantially moved in a direction perpendicular to the direction in which it is moved into the opening. The opening may be formed in a first side of the wall. A second side of the wall, opposite to the first side, may form a wall of the channel. The faceplate portion may be formed with an aperture or opening into which the first side plate is received. The first side plate may move into and out of the aperture when the first flap is moved between its opened and closed positions. The first restricting member may therefore be mounted across the aperture or opening. The body may comprise an exterior body portion for mounting to an exterior side of a door and an interior body portion for mounting to an interior side of the door. The exterior body portion may be secured to the interior body portion by fasteners which pass through the raised portion and the faceplate portion. In this arrangement, the fasteners used to mount the letterplate assembly to the door, wall, or other structure are hidden from view when the first flap is in its closed position, thereby creating an aesthetically pleasing appearance on the interior side of the door. It will be appreciated that, due to the restricted opening angle of the first flap, the first flap may block access to the fasteners used to mount the letterplate assembly to the door, thereby preventing installation or removal of the letterplate assembly when the restricting member is in place. As such, the restricting member can be installed or removed as necessary by screwing or unscrewing the threaded portion into or out of the first part of the body. It will be appreciated that, with the restricting member removed, the first flap can be moved beyond its open position to provide access to the fasteners. The letterplate assembly may be configured such that the fasteners used to secure the interior body portion to the exterior body portion are aligned with the thickness direction of the door, wall, or other structure in which the letterplate is installed. The fasteners may be oriented substantially horizontally in use. The fasteners may be oriented substantially perpendicularly to the first restricting member. The raised portion may be formed by a metal. The metal may be die case zinc, for example, or any other suitable metal. A metal raised portion may provide increased strength and stiffness to the letterplate assembly in the region where the restricting member is fastened to the letterplate assembly. Additionally, a metal raised portion may be advantageous where an exterior body portion of the letterplate assembly is secured to an interior body portion by fasteners which pass through the raised portion, as this may provide the letterplate assembly with increased resistance to attempts to remove the letterplate assembly from the door during an attempted burglary, for example. A metal raised portion may enable the faceplate portion to be constructed from a less costly material and weaker material. For example, the faceplate portion may be formed of a plastic. However, it will of course be appreciated that the raised portion may be formed from any suitable material. The first flap may be prevented from being pivoted beyond the open position by part of the non-threaded portion of the first restricting member abutting with a wall of the opening. In embodiments of the invention, a threaded part of the first restricting member may abut with the first side plate when in the open position. However, this abutment may damage the thread, which may make it difficult to remove and reinstall the first restricting member. It may therefore be advantageous to ensure that the first side plate abuts with a non-threaded part of the first restricting member. The opening in the first side plate may be an elongate slot. The first flap may therefore be prevented from being pivoted beyond the open position corresponding to a maximum opening angle of the first flap by the first restricting member abutting with a wall at an end of the slot of the first side plate. The internal width of the opening or slot may be approximately equal to a cross-sectional dimension of the part of the first restricting member that is received within the opening of the first side plate. However, it may be the case that in embodiments of the invention the first restricting member does not have a uniform cross-sectional dimension along its length. For example, the first restricting member may taper towards its non-threaded end. The first restricting member may have a step-wise change in cross-sectional dimensions along its length. For example, the threaded portion may have a first cross-sectional dimension and the non-threaded portion may have a second cross-sectional dimension, which is smaller than the first cross-sectional dimension. The first side plate slot may be arcuate. Alternatively, the first side plate may be formed with an opening which has a different shape to an arcuate elongate slot. However, such a slot may provide better protection against fishing attacks as the slot can be made relatively narrow to prevent a fishing instrument being passed through the slot. When the first flap is in the open position, the first side plate may fill at least 50% of the angular space between the first flap and the body at the first lateral side of the channel to thereby provide a barrier in the angular space between the first flap and the body at the first lateral side of the channel when the first flap is in the open position. The first side plate may be shaped to fill substantially all of the angular space between the first flap and the body at the first lateral side of the channel. For example, the first side plate may be generally arc shaped in order to substantially fill the angular space between the first flap and the body at the first lateral side of the channel. In embodiments, the first side plate may be generally the shaped like a shark fin with its base mounted to a rear surface of the first flap order to substantially fill the angular space between the first flap and the body at the first lateral side of the channel. In other embodiments, the first side plate is not configured to provide a substantial barrier at the first lateral side of the channel. The first flap may be configured to be pivoted through an angle of no more than 45 degrees between its closed position and its open position. However, the maximum opening angle cannot be overly restricted because the flap must be openable to a position that allows for a range of sizes of post to be posted through the letterplate assembly. In embodiments of the invention, the first flap may be pivotable up to an angle of between approximately 30 degrees and 60 degrees. In a preferred embodiment of the invention, the first flap may be pivotable up to an angle of between approximately 40 degrees and 50 degrees, such as 42 degrees, for example. The head of the first restricting member is configured to receive a hex key. A head configured to receive a hex key, or “alien” key, may be advantageous in embodiments of the invention where fastening the first restricting member using a conventional screwdriver may be difficult due to the position of the head. For example, the head may be positioned such that the hand of a screwdriver operator would clash with a surface of the door (or other structure) into which the letterplate assembly is being installed when attempting to turn the screwdriver. In these scenarios, a conventional L-shaped hex key may be easier to operate in order to fasten the first restricting member. The letterplate assembly may comprise a second restricting member and a second side plate extending from a rear of the first flap at a second opposing lateral side of the channel, the second side plate being formed with an opening, the second restricting member comprising a head, a non-threaded portion, and a threaded portion between the head and the non-threaded portion. The second restricting member may be received within the opening of the second side plate. The second restricting member may be fastened to the body by the threaded portion being engaged with a third part of the body at a first lateral side of the second side plate. The non-threaded portion may be received in a fourth part of the body at a second lateral side of the second side plate, the fourth part of the body being closer to the opening of the channel than the third part of the body. The first flap may be prevented from being pivoted beyond the open position by the second restricting member abutting with a wall of the opening of the second side plate. Alternatively, the opening of the second side plate may be configured differently to the opening of the first side plate such that the second restricting member does not abut with the wall of the opening of the second side plate when the first restricting member abuts with the wall of the opening of the first side plate. For example, the second restricting member and side plate may be configured such that the second restricting member abuts with a wall of the opening of the second side plate only when the first flap is moved beyond its open position, which may happen if the first restricting member is broken or dislodged during an attack on the letterplate assembly. In embodiments, the second side plate and second restricting member may be configured in a substantially identical manner to the first side plate and first restricting member. It will be appreciated that the arrangement of the second side plate and second restricting member may be a mirror image of the first side plate and first restricting member. Any of the features of the letterplate assembly described herein with respect to the first lateral side of the channel may also be present at the second lateral side of the channel. The second side plate may have any of the features described herein with respect to the first side plate. The second restricting member may have any of the features described herein with respect to the first restricting member. The third part of the body may have any of the features described herein with respect to the first part of the body. The fourth part of the body may have any of the features described herein with respect to the second part of the body. According to a second aspect of the invention, there is provided a kit of parts for forming a letterplate assembly according to the first aspect of the invention. The first part of body may comprise a non-threaded hole in which the at least part of the threaded portion of the first restricting member is configured to be fastened. The threaded portion of the first restricting member may be configured cut a thread in the non-threaded hole when fastening the restricting member in the hole. The kit of parts may be provided with a restricting member having a “self-tapping” or “threadcutting” threaded portion which is able to create a thread when fastened into a nonthreaded hole. Removing the step of having to produce a pre-threaded hole in the first part of the body reduces the cost and complexity of the manufacturing process. According to a third aspect of the invention, there is provided a method of assembling a letterplate assembly, the letterplate assembly comprising a first flap, a body, a first side plate, and a first restricting member, wherein the body comprises a channel through which post can be passed from a first side of the letterplate assembly to a second side of the letterplate assembly. The first flap is pivotally mounted to the body at the second side of the letterplate assembly, the first flap being pivotally mounted at or near an upper edge of the first flap, and the first flap being pivotable between an open position and a closed position in which the first flap covers an opening of the channel. The first side plate extends from a rear of the first flap at a first lateral side of the channel, the first side plate being formed with an opening. The method comprises passing a non-threaded portion of the first restricting member through a first part of the body, through an opening in the first side plate, and then into a second part of the body, the second part of the body being closer to the opening of the channel than the first part of the body, and securing the first restricting member to the body by screwing a threaded portion of the first restricting member into the first part of the body, the threaded portion of the first restricting member being situated between the non-threaded portion and a head portion of the first restricting member, the secured first restricting member being configured such that a part of the first restricting member is received within the opening of the first side plate, and the first flap is prevented from opening beyond the open position by the first restricting member abutting with a wall of the opening. The method may comprise passing the non-threaded portion of the first restricting member through a non-threaded hole formed in the first part of the body and securing the first restricting member to the body by screwing the threaded portion of the first restricting member into the non-threaded hole. It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa. Description of the Drawings Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: FIG. 1 shows a door fitted with a letterplate assembly according to an embodiment of the invention; FIG. 2 shows the letterplate assembly in isolation; FIG. 3 is a cross-sectional view of the letterplate assembly wherein the interior body portion and exterior body portion are configured with respect to one another to fit a door having a thickness of 44 millimetres; FIG. 4 is a view of the interior body portion of the letterplate assembly without the interior flap; FIG. 5 is an enlarged view of a part of the interior body portion shown in FIG. 4; FIG. 6 is a cross-sectional view of the interior body portion of the letterplate assembly showing the side plate assembly at the right-hand side of the channel when the interior flap is in a closed position; FIG. 7 is a cross-sectional view of the interior body portion of the letterplate assembly showing the side plate assembly at the right-hand side of the channel when the interior flap is in an open position; FIG. 8 is a partial view of the interior side of the letterplate assembly, with the interior flap removed, showing the position of the pin that acts as a restricting member to restrict the opening angle of the internal flap; FIG. 9 shows the pin that acts as the restricting member to restrict the opening angle of the internal flap; FIG. 10 is a partial perspective view of the interior side of the letterplate assembly; FIG. 11 is a cross-sectional view of the exterior body portion of the letterplate assembly; FIG. 12 is cross-sectional view of the letterplate assembly wherein the interior body portion and exterior body portion are configured with respect to one another to fit a door having a thickness of 63 millimetres and an adjustable member has been placed in the channel to raise the height of the floor of the channel; FIG. 13 shows the adjustable member in isolation; FIG. 14 is a cross-sectional view of the letterplate assembly configured to fit a door having a thickness of 44 millimetres wherein a pole is shown within the letterplate assembly to simulate a fishing attack; FIG. 15 is a cross-sectional view of the letterplate assembly configured to fit a door having a thickness of 63 millimetres wherein a pole is shown within the letterplate assembly to simulate a fishing attack; and FIG. 16 is a perspective cross-sectional view showing the letterplate assembly during a simulated fishing attack. Detailed Description A letterplate assembly 100 according to an embodiment of the invention is shown in FIG. 1 mounted within a letterplate hole of a door 1 of a building. While the letterplate assembly 100 is shown as mounted in a door 2, it will be appreciated that the letterplate assembly 100 could be mounted within a suitable hole in another structure, for example, a wall. The letterplate assembly 100, which is shown in isolation in FIG. 2, comprises an interior body portion 101 connected to an exterior body portion 102. The interior body portion 101 is configured to be mounted within the hole 2 from the interior side of the door 1, whereas the exterior body portion 104 is configured to be mounted within the hole 2 from the exterior side of the door 1. It should be understood that the term “exterior” as used herein is used to refer to the side of the letterplate assembly 100 into which post is received and the term “interior” is used to refer to the side of the letterplate assembly out of which the post passes. It should also be noted that where the terms “vertical”, “horizontal”, “upper”, and “lower” are used in the following description, those terms are used to refer to the orientation of parts of the letterplate assembly 100 when the letterplate assembly is installed horizontally, as shown in FIG. 1, with the width direction of the channel oriented substantially horizontally. As such, those parts may not be oriented as described when the letterplate assembly 100 is not installed, or if the letterplate assembly 100 is installed at some other orientation. With reference to the cross-sectional view of the letterplate assembly 100 shown in FIG. 3, the interior body portion 101 comprises a (vertically extending) interior plate portion 108 which defines an opening 109 through which post and other suitably sized items are received into the building via the letterplate assembly 100. An interior sleeve portion 111 having internal dimensions approximately equal to that of the opening 109 extends (horizontally) from a rear side of the interior plate portion 108 to define a first channel portion 113 A. An interior flap 103 is hinge mounted to the interior plate portion 108 at a location above and adjacent to the opening 109 such that the interior flap 103 completely covers the opening 109 of the interior plate portion 108 when the interior flap 103 is in a closed position, as shown in FIG. 3. The interior body portion 101 further comprises an internal flap 104 which is mounted within the first channel portion 113 A to create a barrier within the first channel portion 113 A. In the presently described embodiment, the internal flap comprises a plastic. However, it will be appreciated that in other embodiments other suitable materials may be used. For example, the internal flap may comprise a metal such as steel. The internal flap 104 is hinge mounted at the ceiling 1131 of the first channel portion 113A, adjacent to the opening 109. The internal flap 104 is formed by a plate that is curved along its vertical height direction such that it curves towards the interior flap 103. In other embodiments of the invention the non-planar shape of the internal flap 104 may be provided in some other way. For example, the internal flap may be formed by a series of two or more linear or non-linear sections. In some embodiments the internal flap 104 may be substantially planar. As can be seen in FIG. 4, on each of its lateral side edges, the internal flap 104 comprises a projecting portion 1040 that extends in the horizontal width direction of the internal flap 104. Each of the projecting portions 1040 is received within a corresponding recess 1132 formed in each of the lateral sidewalls of the channel 113 A. With reference to FIG. 3, each recess 1132 extends in a generally horizontal direction along the length of the channel 113 A and is open at an end that is closest to the interior flap 103 but comprises a wall 1133 at its opposite end. The internal flap 104 is shown in its closed position in FIG. 3. In this configuration, the lower edge 1042 of the interior flap extends out of the opening 109 and does not make contact with the interior plate portion 108. A gap is therefore provided between the lower edge 1042 of the interior flap 104 and the interior plate portion 108 so that thin items, which may not be stiff enough to move the internal flap 104 upon coming into contact with the internal flap 104, can be posted through the letterplate assembly without being crumpled. The internal flap 104 further comprises a rake portion 1043, which can be best seen in FIG. 4 and FIG. 5. The rake portion 1043 is formed by a multiplicity of teeth 1044 which are spaced apart along the width direction W of the internal flap 104, with spaces 1045 provided between neighbouring teeth 1044. The teeth 1044 extend in a generally vertical direction when the internal flap is in its closed position and terminate at the lower edge 1042 of the internal flap 104. Each tooth 1044 has a height Y of approximately 20 millimetres and is substantially V shaped such that the spacing between neighbouring teeth tapers linearly along the height of the tooth. In other embodiments of the invention, the teeth may have some other shape. For example, the teeth may have vertical sides, or sides which curve in a non-linear manner. In the presently described embodiment of the invention, neighbouring teeth are spaced apart such that the spacing X between neighbouring teeth at the lower edge 1042 of the internal flap 104 is approximately 14 millimetres. As can be seen in FIG. 5, the neighbouring teeth are joined at their bases by a curve having a fixed diameter, which is this case is approximately 4 millimetres. It will be appreciated that in other embodiments of the invention, the teeth may have a different height or spacing. Additionally, different teeth may have different heights, alternatively or additionally, different neighbouring teeth may have different spacing therebetween. At each lateral side edge of the interior flap 103 there is a side plate assembly 200 which is configured to abut with a pin 115 to restrict the opening angle A of the interior flap 103. The pin 115 is engaged with a first part of the interior body portion 101 provided by a raised portion 117 and with a second part of the interior body portion provided by a wall 1082. The two side plate assemblies 200 and pins 115 are configured in a substantially identical manner at each lateral side of the opening 109 of the channel 113, so the side plate assemblies 200 will now be described with reference only to the side plate assembly 200 located on the right-hand side of the opening 109, as shown in the figures. With reference to FIG. 6 and FIG. 7, the side plate assembly 200 comprises a primary side plate 201 and a secondary side plate 202. The primary side plate 201 is generally arc shaped and extends from a rear surface of the interior flap 103 in a plane which is generally orthogonal to the rear surface of the interior flap 103. The primary side plate is therefore oriented in a generally vertical plane when the interior flap 103 in its closed position, as shown in FIG. 6. The primary side plate 201 is received in a pocket 114 which is located at a lateral side of the opening 109 such that the primary side plate 201 moves out of and into the pocket 114 as the internal flap 103 is moved between its respective closed and open positions. The primary side plate 201 is formed with an arcuate slot 205 in which a pin 115 is received. The pin 115 is horizontally mounted across the opening 1141 of the pocket 114 into which the side plate assembly 200, as can be best seen in FIG. 8. As illustrated in FIG. 6 and FIG. 7, when the interior flap 103 is moved between its closed and open positions, the pin 115 moves along the slot 205. The interior flap 103 is prevented from being opened by an opening angle A of more than about 42 degrees by the pin 115 abutting the end of the slot 205 furthest away from the interior flap 103. The pin 115 therefore acts as a restricting member that restricts the opening angle A of the interior flap 103, the interior flap 103 being pivotable through an angle of no more than about 42 degrees between its open position and its closed position in which the interior flap 103 covers the opening 109 of the channel 113 A. In other embodiments of the invention, the length of the slot 205 may of course be greater or smaller in order to adjust the maximum opening angle of the interior flap 103. In some embodiments, the opening angle of the interior flap may be restricted by some other means. For example, a part of the interior flap or primary side plate may be configured to abut with the interior body portion to prevent the interior flap being opened beyond a given angle. It will of course be appreciated that in other embodiments of the invention, the interior flap may be restricted to some other opening angle, which may be greater or less than 42 degrees. In some embodiments of the invention, the interior flap may not have a restricted opening angle. The secondary side plate 202 of the side plate assembly 200 has an elongate generally trapezoidal shape and is positioned adjacent the primary side plate 201 in a plane that is generally parallel to the primary side plate 201. As can be seen in FIG. 6, the secondary side plate 202 is sized such that it fits within the planform of the primary side plate 201. The secondary side plate 202 and primary side plate 201 are pivotally connected via a further pin 209 at the distal ends 2011, 2021 of the primary and secondary side plates 201, 202 which are furthest away from the interior flap 103. The secondary side plate 202 comprises a linear slot 207 that runs along a length of the secondary side plate 202 and which also receives the pin 115 that is situated within the slot 205 of the primary side plate 201. The slot 207 in the secondary side plate 202 and pin 115 are configured to control movement of the secondary side plate 202. As can be best seen by a comparison of FIG. 6 and FIG. 7, under the action of gravity on the secondary side plate 202, an upper wall 2071 of the slot 207 rests against the pin 115. As the interior flap 103 is moved from a closed position to an open position, the secondary side plate 202 is moved out of the pocket 114 and rotates downwardly with respect to the primary side plate 201 under the action of gravity and under the control of the pin 115. The pin 115 abuts the upper wall 2071 of the slot 207 to prevent the secondary side plate 202 rotating freely with respect to the first side plate 201. As the secondary side plate 202 rotates downwardly it moves to a position in which the secondary side plate 202 extends below the primary side plate 201 to provide a barrier extending between the interior plate portion 108 and the interior flap 103, below the primary side plate 201. Conversely, as the interior flap 103 is moved from its open position to its closed position, the pin 115 cammingly engages with the upper wall 2071 of the secondary side plate slot 207 to cause the secondary side plate 201 to rotate upwardly with respect to the primary side plate 201. Closing the interior flap 103 therefore lifts the secondary side plate 202 so that can be received in the pocket 114, alongside the primary side plate 201. It should be noted that, while secondary side plate 202 is shown as being positioned between the primary side plate 201 and the opening 109, the secondary side plate 202 could of course be positioned on the other side of the primary side plate 201. It should be noted that the diameter of the pin 115 is approximately equal to the width of the slot 207 such that the pin 115 can only move substantially along the length of the slot. As such, when the interior flap 103 is in a fixed position, for example if the interior flap 103 is held open, the secondary side plate 202 cannot be manually rotated with respect to the primary side plate 201 due to the pin 115 engaging with the upper and lower walls 2071, 2072 of the slot 207. This arrangement may advantageously prevent the secondary side plate 205 being manually lifted by someone trying to access the interior side of the door and, as such, may increase protection against fishing and other attacks at the lateral sides of the letterplate assembly 100, relative to prior art letterplate assemblies. In other embodiments of the invention, the pin 115 may not be present and rotation of the secondary side plate may instead be controlled by the lower edge of the secondary side plate abutting with the lower surface of the pocket, for example. As such, in some embodiments, the secondary side plate may not be formed with a slot. The two pins 115 are configured in a substantially identical manner at each lateral side of the opening 109 of the channel 113, so the pins 115 will now be described with reference only to the pin 115 located on the right-hand side of the opening 109, as shown in the figures. The pin 115, which is shown in isolation in FIG. 9, is a screw pin of the type having a head 1151, a non-threaded portion 1152, and a threaded portion 1153 between the head 1151 and the non-threaded portion 1152. In use, a distal end 1155 of the pin 115 is received in a hole 1081 that can be best seen in FIG. 5. The hole 1081 is formed in a wall 1082 that projects from the interior plate portion 108 between the opening 1141 into which the side plate assembly 200 is received and the opening 109 of the channel 113. The threaded portion 1153 of the pin 115 is received in a raised portion 117 which projects from a surface of the interior plate portion 108 on the opposing lateral side of the opening 1141. The raised portion can be seen in FIG. 8 and FIG. 10 (note that the raised portion 117 has been removed from FIG. 4 and FIG. 5). The raised portion 117 has an elongate cuboidal shape with its longest dimension aligned with the vertical direction. As can be best seen in FIG. 10, the raised portion 117 provides holes through which screws 150 are passed in the thickness direction of the door to fix the interior body portion 101 of the letterplate assembly to corresponding lugs 151 of exterior body portion 102, which can be seen in FIG. 2. One of the functions of the raised portion 117 is to locally strengthen the part of the interior body portion 101 in which the screws 150 are fixed in order to increase the force needed to forcibly remove the letterplate assembly from the door by, for example, trying to pull the exterior body portion 102 away from the interior body portion 101. In the presently described embodiment of the invention, the raised portions 117 are formed from die cast zinc. However, in other embodiments of the invention the raised portions may be formed from other suitable materials such as, for example, polymers or other metals. A second function of the raised portion 117 is to provide a fixing point for the threaded portion 1153 of the pin 115. As can be best seen in FIG. 8, in use, the threaded portion 1153 of the pin 115 is contained within the raised portion 117 and the distal end 1155 is located in the wall 1082 that projects from the interior plate portion 108. A part of the unthreaded portion 1152 is situated in the space between the raised portion 117 and the wall 1082. As can be seen in FIG. 10, the nonthreaded portion 1152 of the pin 115 is received in the slot 205 of the primary side plate 201 and the slot 207 of the secondary side plate 202. In embodiments of the invention, a threaded part of the pin 115 may abut with the side plates 201, 202 when in the open position. However, this abutment may damage the thread, which may make it difficult to remove and reinstall the pin. It may therefore be advantageous to ensure that the side plates abut with a non-threaded part of the pin. The exterior body portion 102, which is shown in isolation in FIG. 11, comprises an exterior plate portion 106 which defines an opening 105 and an exterior sleeve portion 112 which projects from the rear-side of the exterior plate portion 106. The exterior sleeve portion 112 is dimensioned to be received within the interior sleeve portion 111, as can be seen in the cross-sectional view of FIG. 3. An exterior flap 107 is hinge mounted to the exterior plate portion 106 at a location above and adjacent the opening 105 such that the exterior flap 107 completely covers the opening 105 of the exterior plate portion 106 when the exterior flap 107 is in a closed position. The exterior sleeve portion 112 defines a second channel portion 113B. When the exterior body portion 102 is assembled together with the interior body portion 101 their respective first and second channel portions 113 A, 113B form a channel 113 between the opening 105 of the exterior body portion 102 and the opening 109 of the interior body portion 101. The floor 1135 of the second channel portion 113B comprises a raised portion 118, which spans the width of the interior first channel portion 113B. The raised portion 118 comprises a sloping surface 1181 configured such that the height of the raised portion 118 increases with increasing distance from the exterior flap 107. The sloping surface 1181 of the raised portion 118 helps guide items of post through the letterplate assembly 100 and may prevent the items of post snagging or being otherwise hindered by the raised portion 118. The raised portion 118 defines the maximum height H of the floor of the channel 113, which is the vertical distance between the uppermost surface of the raised portion 118 and the lowest point on the floor, which in this case is the substantially planar floor surface 1136 provided by the first channel portion 113A, as indicated in FIG. 3. The maximum height of the floor H can be further increased by placing an adjustable member 300 within the second channel portion 113B, as shown in FIG. 12. The adjustable member 300 is arranged contiguously with the raised portion 118 on the side of the raised portion 118 that is closest to the interior flap 103. When the adjustable member 300 is installed, it effectively forms an extension of the raised portion 118 and partially forms the floor 1135 of the second channel portion 113B. It should be noted that the raised portion 118 or, when installed, the adjustable member 300 also define the location within the channel 113 at which the internal height of the channel 113 is a minimum, the minimum internal height of the channel 113 being the distance between the uppermost surface of the raised portion 118 or adjustable member 300 and the ceiling 1137 of the channel. It will be appreciated that the minimum internal height of the channel limits the maximum thickness of items of post which can be passed through the channel 113. Generally, the minimum internal height of the channel should be dimensioned to allow post having a thickness of at least 20 millimetres to 30 millimetres to be posted through the channel 113. The adjustable member 300, which is shown in isolation in FIG. 13, comprises an elongate bar 301 having a length approximately equal to the internal width of the second channel portion 113B. The elongate bar 301 has a curved profile that is shaped to raise the effective floor 1135 of the second channel portion 113B to a height above the raised portion 118, such that the maximum height of the floor H is greater than when the adjustable member 300 is not present, as can be seen by comparison of FIG. 11 and FIG. 12. The adjustable member 300 also comprises a sloping surface 302 configured such that initially the height of the adjustable member 300 increases with increasing distance from the exterior flap 107. The sloping surface 302 of the adjustable member 300 is arranged contiguously with the raised portion 118 and may help guide items of post through the letterplate assembly 100 by preventing the items of post snagging or being otherwise hindered by the adjustable member 300. As can be seen in FIG. 12, the adjustable member 300 is held in place within the second channel portion 113B by horizontally oriented screws 400. The screws 400 pass through holes 303 formed in tabs 305 which extend from the elongate bar 301 and towards the floor 1135 of the second channel portion 113B. The holes 303 in the adjustable member 300 are elongated in the vertical direction, as can be seen in FIG. 13, such that the elongate bar 301 can be raised or lowered and fixed at a desired vertical position to select the desired maximum height H of the floor of the channel 113. While the internal height of the channel 113 can be adjusted by raising or lowering the adjustable member 300, in other embodiments of the invention adjustable members having different heights may be provided so that the height of the floor of the channel may be set by installing an adjustable member having a suitable height. Various features of the letterplate assembly 100 described above are provided to mitigate fishing attacks and manipulation of the parts of the door lock on the interior side of the door. The angle to the horizontal with which a fishing instrument 500, for example a pole, can be inserted through the letterplate assembly 100 is controlled by controlling the contact points that the instrument 500 makes with the letterplate assembly when inserted into the channel 113. Controlling the angle at which a fishing instrument can be passed into a building is advantageous because it controls the reach of the fishing instrument. FIG. 14 shows the letterplate assembly 100 configured for use on a door having a thickness T of approximately 44 millimetres and with a pole 500 inserted through the channel to simulate a fishing attack. In this configuration, the closest the pole can get to the horizontal is an angle B of approximately 19 degrees because the pole is prevented from moving further towards the horizontal by its abutment with the lower edge 1031 of the interior flap 103, which has a restricted opening angle, on an upper side 501 of the pole 500 and with the raised portion 118 on the lower side 502 of the pole 500. The letterplate assembly 100 can of course be installed on doors having different thicknesses. Installation of the letterplate assembly on a thicker door will move the raised portion 118 further away from the interior flap 103, which will reduce the angle B that a fishing tool is able to make to the horizontal by virtue of the contact points that limit the angle that a fishing tool can make with the horizontal being moved further apart. In order to limit the reach of a potential fishing attack on thicker doors, the adjustable member 300 can be installed. FIG. 15 shows the letterplate assembly 100 as installed on a thicker door having a thickness T of approximately 63 mm with the adjustable member 300 in place. It should be noted that the exterior plate portion 106 and the interior plate portion 108 are spaced further apart than shown in FIG. 14 to accommodate for the increased thickness of the door. With the adjustable member 300 in place, an upper side 501 of the fishing instrument 500 abuts with the lower edge 1031 of the interior flap 103 and the uppermost surface 301 of the adjustable member 300 abuts the lower side 502 of the pole 500. With the adjustable member 300 installed as shown in FIG. 15 on a door having a thickness T of approximately 63 mm, the smallest angle B that the pole 500 can make with the horizontal can therefore be maintained at a value similar to that of when the thickness T of the door is approximately 44 millimetres (in FIG. 15 the angle B is approximately 17 degrees). Of course, the height H of the floor of the channel 113 can be adjusted by adjusting the vertical position of the adjustable member 300 in order to accommodate different door thicknesses, or to change the angle with which a fishing tool can make with the horizontal for a given door thickness. It should be noted that the height V of the interior flap 103, indicated in FIG. 2, is approximately 100 millimetres in the presently described embodiment of the invention. However, in other embodiments of the invention the height V of the interior flap may be different and, as such, the lower edge of the interior flap, which provides a contact point for a fishing instrument during a fishing attack, may be at a different position with respect to the contact point provided by a raised member or adjustable member. As can be best seen in FIG. 7 and FIG. 10, the side plate assemblies 200 close off the spacing between the interior flap 103 and the interior plate portion 108 to provide protection at the lateral sides of the opening 109. In particular, the secondary side plate 202 extends below the primary side plate 201 to reduce the degree to which the pole 500 can be manipulated into a position at the sides of the letterplate assembly 100. The secondary plate 202 thereby improves protection, when compared to an arrangement comprising only a primary side plate 201. The difficulty of successfully making a fishing attack is further increased by the provision of the internal flap 104 having a rake portion 1043, as illustrated by FIG. 16. During a fishing attack, a fishing instrument 500, such as a pole, may become lodged in a space 1045 between neighbouring teeth 1044 of the internal flap 104. Upon removal of a fishing tool 500 from the letterplate assembly 100, an article successfully retrieved in the fishing attack, for example a key 600, may then be caught between the teeth 1044 of the rake portion 1043 as the pole 500 is pulled out of the channel 113. The internal flap 104 will be prevented from moving substantially beyond its closed position, shown in FIG. 3 and FIG. 12, by the projecting portions 1040 of the internal flap 104 abutting with the end walls 1133 of the recesses 1132. As such, the key 600 may be captured between the teeth 1044 and become dislodged from the fishing tool 500 by the teeth 1044 as the fishing tool is pulled out of the letterplate assembly 100. Because the height of the internal flap 104 is less than the internal height of the first channel portion 113 A, the internal flap 104 could, in the absence of the projecting portions 1040, be rotated into the first channel portion 113A, anticlockwise in the orientation of the letterplate assembly 100 as shown in FIG. 3, by someone trying to tamper with the letterplate assembly 100. As explained above, in the event that someone tries to rotate the internal flap 104 into the channel 113 A, the projecting portions 1040 of the internal flap 104 will abut with the end walls 1133 of the recesses 1132. In some embodiments, the internal flap may have a greater height such that it extends below the lower edge of the channel and abuts with the lower edge of the channel in the event that someone tries to rotate the lower flap into the channel. In other embodiments of the invention, the letterplate assembly is not be configured to prevent rotation of the flap into the channel. The opening angle A of the interior flap 103 is restricted by the pin 115 which, in use, is located in the slots 205, 207 of the respective primary and secondary side plates 201, 202. The pin 115 acts as a restricting member which abuts with an end of the slot 205 in the primary side plate 202 to prevent the interior flap 103 being opened beyond its open position shown in FIG. 7. As can be best seen in FIG. 2 and FIG. 10, the interior body portion 101 is fixed to the exterior body portion 102 by screws 150 that pass through the raised portions 117 of the interior body portion 101 and engage with lugs 151 which form part of the exterior body portion 102. The interior flap 103 covers the raised portion 117 when in the closed position such that the raised portion 117 and pin 115 are hidden from view, thereby providing the interior side of the letterplate assembly 100 with an aesthetically pleasing appearance. However, as can be best seen in FIG. 10, with the pin 115 in place and the opening angle A of the interior flap 103 restricted, the interior flap 103 obstructs access to the heads of the screws 150. The letterplate assembly 100 must therefore be secured to the door 1 with the interior flap 103 in an unrestricted configuration before the pin 115 is installed. As such, the pin 115 must be installed by the person securing the letterplate assembly 100 to the door 1, rather than it being preinstalled. The use of a screwpin as the pin 115 is particularly advantageous for ensuring correct installation of the pin 115 once the letterplate assembly 100 is secured to the door 1. As described above, the threaded portion 1153 of the pin 115 engages with a hole formed in the raised portion 117 through which the screws 150 used to secure the interior body portion 101 to the exterior body portion 102 pass. The raised portion 117 is formed from a metal in order to provide a relatively strong fixing point for the screws 150 and therefore also provides a convenient part of the exterior body portion 102 to which the pin 115 can be securely fastened. In the presently described embodiment, the raised portion 117 is provided with an unthreaded hole and the pin 115 is provided with a self-tapping thread that cuts a thread in the raised portion 117 as the unthreaded portion 1153 is screwed into the hole in the raised portion 117. Once the interior body portion 101 has been fastened to the exterior body portion 102 by engaging the screws 150 with their respective lugs 151, to install the pins 115, the interior flap 103 must be opened to a position in which the unthreaded portion 1152 of the pin 115 can be passed through the hole in the raised portion 117 and into the slot 205 of the primary side plate 201. The secondary side plate 202 must be moved to a position in which the distal end 1155 of the pin 115 can then be passed through the slot 207 in the secondary side plate 202 after being passed through the slot 205 of the primary side plate 201. The threaded portion 1153 is then screwed into the hole formed in the raised portion 117 in order to move the distal end 1155 of the pin 115 into the hole 1081 formed in the wall 1082 that projects from the interior plate portion 108. As can be seen in FIG. 8 and FIG. 10, the hole into which the pin 115 is screwed is countersunk on the outer lateral side 1171 of the raised portion 117 so, for correct installation, the pin 115 must simply screwed into the raised portion 117 as far as it will go, until the top of its head 1151 is flush with the outer lateral side 1171 of the raised portion. The use of a screwpin having a non-threaded distal end 1155 as the pin 115 means that the distal end 1155 slides into the hole 1081 formed in the wall 1082; this arrangement is particularly advantageous over other fasteners, in particular those with threaded tips because it ensures that the pin 115 can be easily installed securely at the correct depth without over-tightening the pin 115. If the distal end of the pin were threaded and configured to be screwed into the wall 1082, there is a risk that the pin could be over-tightened during the installation process, which could result in the wall 1082 being pulled towards the raised portion 117 by the threaded distal end of the pin as the pin is overtightened, which in turn could lead to the side plate assembly 200 being compressed between the wall 1082 and the raised portion 117, restricting free movement of the interior flap 103. Furthermore, as can be best seen in FIG. 9, the head 1151 comprises a hexagonal recess configured to receive a hex key, or Allen key, so that a traditional L-shaped hex key can be used to fasten the pin 115. When the letterplate assembly 100 is secured to the door, the head 1151 of the pin 115 sits very close to the surface of the door 1, which would make screwing the pin into the raised portion 117 with a traditional screwdriver difficult due to the low clearance between the handle of the screwdriver and the surface of the door. The use of an L-shaped hex key for fastening the pin 115 is therefore particularly advantageous because it has a part that will project perpendicularly away from the part that is engaged with the head 1151 so that the hex key can be turned without being impeded by the door. Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. In particular, the letterplate assembly 100 described above has the following optional features that mitigate attacks on the letterplate assembly by someone trying to access the interior side of door: the height of the floor of the channel of the letter plate assembly can be adjusted to control the angle at which a fishing instrument can be inserted through the channel, side plate assemblies provide protection against fishing attacks at the lateral sides of the interior flap, and an internal flap having a rake portion helps prevent fished items from being retrieved through the channel. The invention relates to a letterplate assembly comprising a restricting member that is particularly advantageous for assembling the letterplate assembly. The restricting member has a head, a non-threaded portion, and a threaded portion between the head and the non-threaded portion, and is not limited to the specific embodiments described herein. Embodiments of the invention include letterplate assemblies having only primary side plates, rather than side plate assemblies comprising both primary and secondary side plates. Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

1. A letterplate assembly comprising a first flap, a body, a first side plate, and a first restricting member, whereinthe body comprises a channel through which post can be passed from a first side of the letterplate assembly to a second side of the letterplate assembly,the first flap is pivotally mounted to the body at the second side of the letterplate assembly, the first flap being pivotally mounted at or near an upper edge of the first flap, the first flap being pivotable between an open position and a closed position in which the first flap covers an opening of the channel,the first side plate extends from a rear of the first flap at a first lateral side of the channel, the first side plate being formed with an opening,the first restricting member comprises a head, a non-threaded portion, and a threaded portion between the head and the non-threaded portion,the first restricting member is received within the opening of the first side plate, the first flap being prevented from pivoting beyond the open position by the first restricting member abutting with a wall of the opening,the first restricting member is fastened to the body by the threaded portion being engaged with a first part of the body at a first lateral side of the first side plate, andthe non-threaded portion of the first restricting member is received in a second part of the body at a second lateral side of the first side plate, the second part of the body being closer to the opening of the channel than the first part of the body.

2. A letterplate assembly according to claim 1, wherein the head of the first restricting member abuts the first part of the body.

3. A letterplate assembly according to claim 1 or claim 2, wherein the body comprises a faceplate portion which defines the opening of the channel, the first part of the body comprises a raised portion which projects from a surface of the faceplate portion at the first lateral side of the channel, the threaded portion is engaged with the raised portion, and the first flap covers the raised portion and the head of the restricting member when in the closed position.

4. A letterplate assembly according to claim 3, wherein the body comprises an exterior body portion for mounting to an exterior side of a door and an interior body portion for mounting to an interior side of the door, and wherein the exterior body portion is secured to the interior body portion by fasteners which pass through the raised portion and the faceplate portion.

5. A letterplate assembly according to any of claims 2 to 4, wherein the raised portion comprises a metal.

6. A letterplate assembly according to any of claims 1 to 5, wherein the first flap is prevented from being pivoted beyond the open position by part of the nonthreaded portion of the first restricting member abutting with a wall of the opening.

7. A letterplate assembly according to any of claims 1 to 6, wherein the opening in the first side plate is an elongate slot.

8. A letterplate assembly according to any of claims 1 to 7, wherein, when the first flap is in the open position, the first side plate fills at least 50% of the angular space between the first flap and the body at the first lateral side of the channel to thereby provide a barrier in the angular space between the first flap and the body at the first lateral side of the channel when the first flap is in the open position.

9. A letterplate assembly according to any of claims 1 to 8, wherein the first flap is configured to be pivoted through an angle of no more than 45 degrees between its closed position and its open position.

10. A letterplate assembly according to any of claims 1 to 9, wherein the head of the first restricting member is configured to receive a hex key.

11. A letterplate assembly according to any of claims 1 to 10, further comprising a second restricting member and a second side plate extending from a rear of the first flap at a second opposing lateral side of the channel, the second side plate being formed with an opening,the second restricting member comprises a head, a non-threaded portion, and a threaded portion between the head and the non-threaded portion, the second restricting member is received within the opening of the second side plate,the second restricting member is fastened to the body by the threaded portion being engaged with a third part of the body at a first lateral side of the second side plate,the non-threaded portion is received in a fourth part of the body at a second lateral side of the second side plate, the fourth part of the body being closer to the opening of the channel than the third part of the body.

12. A kit of parts configured to form a letterplate assembly according to any of claims 1 to 11.

13. A kit of parts according to claim 12, wherein the first part of body comprises a non-threaded hole in which the at least part of the threaded portion of the first restricting member is configured to be fastened and the threaded portion of the first restricting member is configured cut a thread in the non-threaded hole when fastening the restricting member in the hole.

14. A method of assembling a letterplate assembly, the letterplate assembly comprising a first flap, a body, a first side plate, and a first restricting member, wherein the body comprises a channel through which post can be passed from a first side of the letterplate assembly to a second side of the letterplate assembly,the first flap is pivotally mounted to the body at the second side of the letterplate assembly, the first flap being pivotally mounted at or near an upper edge of the first flap, and the first flap being pivotable between an open position and a closed position in which the first flap covers an opening of the channel, andthe first side plate extends from a rear of the first flap at a first lateral side of the channel, the first side plate being formed with an opening,wherein the method comprises passing a non-threaded portion of the first restricting member through a first part of the body, through an opening in the first side plate, and then into a second part of the body, the second part of the body being closer to the opening of the channel than the first part of the body, and securing the first restricting member to the body by screwing a threaded portion of the first restricting member into the first part of the body, the threaded portion of the first restricting member being situated between the non-threaded portion and a head portion of the first restricting member, the secured first restricting member being configured such that a part of the first restricting member is received within the opening of the first side plate, and the first flap is prevented from opening beyond the open position by the first restricting member abutting with a wall of the opening.

15. The method of claim 14, wherein the method comprises passing the nonthreaded portion of the first restricting member through a non-threaded hole formed in the first part of the body and securing the first restricting member to the body by screwing the threaded portion of the first restricting member into the non-threaded hole.

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