Patent Description:
It is known to cover the pin during storage in order to protect it from impacts or corrosion. Typically, the protection devices used are difficult to install on the pin. There is therefore a need for a simple, easy to assemble protector assembly.

<CIT> describes a pipeline rapid-plugging device which is provided with a press-against flange and a pipe cap flange. <CIT> describes a universal thread protector is provided for protecting either of the pin and box ends of a pipe. <CIT> describes a sealing device for sealing a free end of a generally tubular object.

Accordingly, the following describes a protector assembly for covering a pin of a threaded pipe, comprising a cover, a retainer and at least one fastener for fastening the retainer to the cover, wherein: the cover includes a tubular portion defining a longitudinal axis from a closed end to an open end, the open end defining a rim for axial abutment with the retainer; the retainer has an abutment face for abutment with the rim; the rim comprises a bore extending therethrough; a fastener extends through the bore of the rim and engages the retainer, the fastener extending substantially in parallel with the longitudinal axis and exposed on the cover side of the bore of the rim for engagement by a tool or user to operate the fastener and wherein: the fastener threadably engages with the bore of the retainer; or the fastener engages the surface of the retainer.

There is also described a method of assembling a protector assembly on a pin of a threaded pipe, comprising the steps of: covering the pin of the threaded connector with a cover having a closed end and an open end defining a rim; engaging the pipe body with a retainer such that the retainer surrounds the pipe body; inserting a threaded fastener through the rim of the cover from the closed end side; and threadably engaging the retainer with the threaded fastener.

When a large number of pipes are stacked for storage or transport, an operator can use the assemblies and methods described herein to cover the end of the pins in the middle of the stack. Using conventional pin covers, this would require reaching awkwardly past the end of the pin to use a tool that will extend perpendicular to the pipe. Of course, when the pipe is in a stack, the use of such a tool is hindered by the neighbouring pipes. The described assemblies and methods can enable an operator to easily cover a pin of a threaded pipe merely accessing the assembly from the cover side, without needing to reach around the cover or use a tool other than at the cover side of the assembly.

For a better understanding of the invention, and to show how the same may be put into effect, reference will now be made, by way of example only, to the accompanying drawings in which:.

<FIG> show a first embodiment of a protector assembly <NUM> installed on a pipe <NUM> in accordance with the invention.

As is conventional in the oil and gas industry, the pipe <NUM> terminates in a pin <NUM> having a male thread for engagement with a female thread of a box. The protector assembly <NUM> does not include the pipe <NUM>, but forms a pipe/protector assembly when installed thereon.

The protector assembly <NUM> comprises a cover <NUM>, a retainer <NUM> and at least one fastener <NUM>.

The cover <NUM> and the retainer <NUM> may be made from plastics, such as polyethylene (e.g., HDPE) or polypropylene.

The cover <NUM> comprises a tubular portion <NUM> defining a longitudinal axis from a closed end <NUM> to an open end <NUM>, the open end <NUM> defining a rim <NUM> for axial abutment with the retainer <NUM>.

The rim <NUM> may be a radial extension around the perimeter of the cover <NUM>.

The tubular portion <NUM> and closed end <NUM> are sized and shaped for covering the pin <NUM> of a pipe <NUM>. In preferred embodiments, the closed end <NUM> is therefore a circular disc at the end of the tubular portion <NUM>, which is cylindrical, frustoconical, or a combination of cylindrical and frustoconical sections.

Preferably, when intended for covering a pin <NUM> with a tapered thread, the tubular portion <NUM> includes a tapered section, which tapers at the same angle as the thread of the pin <NUM>. The end of the pin <NUM> may abut the inside of the cover <NUM>.

For example, the cover <NUM> may have an inner surface that is approximately the same shape as at least a portion of the outer surface of the pin <NUM> that it is intended to cover.

Optionally, the cover <NUM> comprises an internal coupling thread <NUM> for engagement with a pin <NUM>. The internal coupling thread <NUM> may be formed on the inner surface of the tubular portion <NUM>.

Surface features <NUM> may be provided on the outer surface of the closed end <NUM> for engaging a tool for rotating the cover <NUM>. This can assist, in particular, for removing the cover <NUM> from the pin <NUM>.

The rim <NUM> has an abutment face <NUM> for abutment with the retainer <NUM>. The rim <NUM> comprises one or more bores <NUM> extending therethrough. The bores <NUM> of the rim <NUM> may or may not be threaded.

The retainer <NUM> is arranged to extend radially closer to the longitudinal axis than the rim <NUM>. In this way, when the retainer <NUM> is fastened to the cover <NUM> by the fastener <NUM>, the retainer can engage a part of the pin <NUM>, such as a shoulder <NUM>, that the rim <NUM> would not engage.

The retainer <NUM> has a circular opening <NUM> and an abutment face <NUM> perpendicular to the longitudinal axis (the longitudinal axis extends through the centre of the circular opening <NUM> and perpendicular to the plane of the circle) for abutment with the abutment face <NUM> of the rim <NUM>. Preferably, the retainer <NUM> is ring-shaped.

The retainer <NUM> comprises one or more bores <NUM> extending into the abutment face <NUM>. For assisting with the alignment of a fastener <NUM> during insertion, a tapered opening <NUM> may be provided in the abutment face <NUM> to guide the fastener <NUM> into the bore <NUM>. The bores <NUM> of the retainer correspond with those of the cover <NUM>.

Preferably, the retainer <NUM> comprises a threaded bore <NUM>.

The retainer <NUM> may be formed of a single material having the bores <NUM> formed therein, such that it is free of inserts. Alternative, inserts such as nuts may be provided to define the (or a part of the) bores <NUM>. Such inserts would preferably be rotationally held within a main body part of the retainer <NUM>. This may be achieved, for example, by having a non-circular shaped cut out (such as a hexagon) complementary to an outer surface of the insert within the main body part of the retainer <NUM> within which the inserts are held.

In preferred embodiments, the retainer <NUM> includes a first end <NUM> and a second end <NUM>.

When installed on a pipe <NUM>, the first end <NUM> and the second end <NUM> meet at an overlap section <NUM>. In the overlap section <NUM>, the ends <NUM>, <NUM> overlap circumferentially. That is, the retainer <NUM> from first end <NUM> to second end <NUM> extends more than <NUM> degrees around the pipe <NUM>.

The bore <NUM> of the retainer <NUM> may extend through the overlap section <NUM> for enabling a single fastener <NUM> to both engage the cover <NUM> with the retainer <NUM>, and engage the first end <NUM> with the second end <NUM>.

Preferably, the bore <NUM> is threaded throughout both of the first and second ends <NUM>, <NUM>. However, in some embodiments, the fastener <NUM> extends through the bore <NUM> through first end <NUM> without threadingly engaging the first end <NUM>, and threadably engages the bore <NUM> through the second end <NUM> to fasten together the first and second ends <NUM>, <NUM>. In these examples, the second end <NUM> is further from the cover <NUM> than the first end <NUM> (that is, the first end <NUM> is held between the cover <NUM> and the second end <NUM> on the fastener <NUM>).

In one preferred embodiment, the retainer <NUM> is a split ring as shown in <FIG>. That is, the retainer <NUM> is a single, continuous piece of material between the first and second ends <NUM>, <NUM>. The retainer may be made of a resilient material such that it can be elastically deformed to separate the first and second ends <NUM>, <NUM> so that the pipe body <NUM> can be inserted therebetween.

In another preferred embodiment, the retainer <NUM> is a ring assembly comprising a first part 200a having the first end <NUM> and a second part 200b having the second end <NUM>. The first and second parts 200a, 200b can collectively surround a pipe <NUM>. For example, the first and second parts 200a, 200b may be arc-shaped , or generally arc-shaped.

The first and second ends <NUM>, <NUM> meet to form overlap section <NUM>. The other ends of the first and second parts 200a, 200b meet to form a further overlap section <NUM>. Alternatively, the retainer <NUM> may include a hinge such that it can be opened and closed around the pipe <NUM>. In such cases, the hinge is not necessarily fastened by a fastener extending through the cover <NUM>.

As will be appreciated, it is not necessary that a retainer <NUM> formed as a ring assembly be limited to two parts. Multiple parts may be provided. As shown in <FIG>, three (or more) parts 200a, 200b, 200c may be provided to collectively surround a pipe <NUM> providing an overlap section <NUM> between the first and second ends <NUM>, <NUM> of two of the parts 200a, 200b, and further overlap sections <NUM> between other ends of the parts 200a, 200b, 200c. For example, the three or more parts 200a, 200b, 200c may be arc-shaped , or generally arc-shaped.

Preferably, the other overlap sections <NUM> have the same configuration as the overlap section <NUM> of the first and second ends <NUM>, <NUM>.

As best shown in <FIG>, the first and second ends <NUM>, <NUM> are shaped so as to define interfitting shoulders that abut in the circumferential direction (that is, the direction around the perimeter of the pipe <NUM>) and overlap to form the overlap section <NUM>.

In the particular example shown in <FIG>, the first end <NUM> of the retainer <NUM> has a recess <NUM> shaped to receive the second end <NUM>, while the second end <NUM> has a recess shaped to receive the first end <NUM>.

The recess of the first end <NUM> may form an internal shoulder having a surface <NUM> for circumferential abutment with the tip <NUM> of the second end <NUM>, and a surface <NUM> for longitudinal abutment (i.e., perpendicular to the circumferential direction, in line with the longitudinal direction of the cover <NUM> when the protector assembly <NUM> is assembled) with a complementary surface <NUM> of the second end <NUM>. The second end <NUM> is formed in a complementary way, with an internal shoulder having a circumferential abutment surface <NUM> for abutting the tip <NUM> of the first end <NUM> and a surface <NUM> for longitudinal abutment with the complementary surface <NUM> of the first end <NUM>.

Other configurations are possible, however, it is preferable that the first and second ends <NUM>, <NUM> are shaped for abutment both circumferentially and longitudinally.

The terms ring-shaped and ring assembly are not intended to limit the shape of the item to a strict torus, but merely mean to denote an item that can extend around the perimeter of the pipe.

The rim <NUM> may include a notch <NUM>, for example in the abutment face <NUM> (as shown), and the retainer <NUM> may include a projection <NUM>, located for engagement with the notch <NUM>. In the alternative, the rim <NUM> may include a projection (for example in the same location as the notch is shown), and the retainer <NUM> may include a notch <NUM>. In either case, the notch and projection may be located such that when they are engaged, the bores <NUM>, <NUM> of the cover <NUM> and the retainer <NUM> are aligned. In particular, the cover <NUM> and the retainer <NUM> are rotationally aligned about the longitudinal axis, when the notch <NUM> and projection <NUM> are engaged.

The fastener <NUM> fastens the cover <NUM> to the retainer <NUM>. The fastener <NUM> is exposed on the cover side of the bore of the rim such that it may be engaged by a tool or user to operate the fastener. For example, the tool could be a screwdriver that operates the fastener <NUM> by rotating it. Such rotation can operate the fastener <NUM> by threadably engaging the fastener <NUM> with the bore <NUM>.

Preferably, the fastener <NUM> comprises a head portion <NUM> and a threaded portion <NUM>, and optionally a stem portion <NUM>. The stem portion <NUM> may be unthreaded. In some embodiments, the head portion <NUM> of the fastener <NUM> may have a greater outer diameter than the diameter of bore <NUM>.

Preferably, the head portion <NUM> is shaped for rotational engagement by a tool. That is, a tool (such as a screwdriver or Allen key) may be engaged with the head portion <NUM> so that rotation of the tool rotates the fastener <NUM> and thereby engages or disengages the fastener <NUM> from the retainer <NUM>.

The head portion <NUM> is at one end of the fastener <NUM> and the threaded portion <NUM> is at the opposite end of the fastener <NUM>. The stem portion <NUM>, when provided, links the head portion <NUM> to the threaded portion <NUM>. When no stem portion <NUM> is provided, the threaded portion <NUM> extends all the way to the head portion <NUM>.

When the protector assembly <NUM> is assembled, the bore <NUM> of the cover <NUM> aligns with the bore <NUM> of the retainer <NUM>. The fastener <NUM> extends through the bore <NUM> of the rim <NUM> for threadable engagement with the bore <NUM> of the retainer <NUM>.

The bore <NUM> through the retainer <NUM> is preferably formed in the material of the first and second ends without the provision of any form of insert made of different material.

In some embodiments, the fastener <NUM> threadably engages the bore <NUM> of the rim <NUM> as well as the bore <NUM> of the retainer <NUM>. In such cases, no stem portion <NUM> is needed.

However, for speed of assembly, it is preferred that the bore <NUM> of the rim <NUM> does not include threads and is sized for the threaded portion <NUM> of the fastener <NUM> to be slid therethrough without the threads engaging the cover <NUM>.

When the fastener <NUM> is fully inserted into the cover <NUM> (whether threadably engaged therewith or simply slid through), the threaded portion <NUM> extends beyond the abutment surface <NUM> of the rim <NUM>. This protruding section of the fastener <NUM> can threadably engage the bore <NUM> of the ring assembly <NUM>.

A counter bore or counter sink <NUM> may be provided such that the head <NUM> of the fastener <NUM> is within the rim <NUM> when the protector assembly <NUM> is assembled. Alternatively, the head <NUM> of the fastener <NUM> may be outside the rim <NUM>. In either case, it is preferred that, when the protector assembly <NUM> is assembled, the head portion <NUM> is exposed on the closed end side of the rim <NUM> for engagement with a tool. As can be seen in <FIG>, the head portion <NUM> is exposed such that it is accessible from the closed end side of the cover <NUM>.

Whilst above is described a single fastener <NUM>, depending on the circumference of the pipe <NUM>, it is preferable to provide more than one fastener <NUM>. In preferred embodiments, the protector assembly <NUM> includes a plurality of fasteners, spaced around the periphery of the rim <NUM>.

In embodiments in which the retainer <NUM> is formed as a ring assembly having a plurality of parts meeting at an overlap section <NUM> and one or more further overlap sections <NUM>, it is preferable to provide a fastener <NUM> for each overlap section <NUM>, <NUM>. In particular, it is preferable to fasten each of the further overlap sections <NUM> with a fastener <NUM> in the same manner as the overlap section <NUM> shown in <FIG> and described in connection therewith. Optionally, additional fasteners <NUM> may be provided to extend through the cover <NUM> and threadably engage the retainer <NUM> at a location other than at an overlap <NUM>, <NUM>.

In embodiments in which the retainer <NUM> is formed as a split ring, as shown in <FIG>, additional fasteners <NUM> may be provided to extend through the cover <NUM> and threadably engage the retainer <NUM> at one or more spaced apart locations other than at an overlap <NUM>, <NUM>. Such additional fasteners <NUM> may extend into threaded bores <NUM> through single parts of the retainer <NUM>.

As shown in the figures, the protector assembly <NUM> forms a pipe protector assembly when installed on the pipe <NUM>. The pipe protector assembly <NUM> comprises the cover <NUM>, the retainer <NUM>, the at least one fastener <NUM>, and the pipe <NUM>.

The pipe <NUM> includes a pipe body <NUM>, which extends to the pin <NUM>.

The pin <NUM> includes a terminal abutment surface <NUM> at the extreme end of the pipe <NUM> for abutment with the inside of the cover <NUM>.

Preferably, the pin <NUM> will have a tapered thread <NUM> for engagement with a female thread of a box and for engagement with a complementary thread <NUM> if this is formed on the internal surface of the cover <NUM>. In such cases, the tubular portion <NUM> includes a tapered section, which tapers at the same angle as the thread of the pin <NUM>. The inner surface of the tubular portion <NUM> may simply be smooth and overly the crests of the pin thread <NUM>, or (as shown in the Figures) an internal coupling thread <NUM> may be formed on the inner surface of the tubular portion <NUM> for engagement with the thread <NUM> of the pin <NUM>.

The pin <NUM> may have one or more shoulders <NUM>, <NUM> along its length for axial abutment. For example, a forward facing shoulder <NUM> (forward facing meaning facing towards the terminal end of the pin <NUM>) may be provided for abutting an internal shoulder of a box.

As another example, the rear surface of the pin <NUM> may be formed with a rear facing shoulder <NUM> (rear facing meaning facing away from the terminal end of the pin <NUM>). The rear facing shoulder may be without utility in connecting the pin <NUM> to a box, but can be used for abutment with the retainer <NUM>.

The cover <NUM> may comprise an internal shoulder <NUM> for abutment with the forward facing shoulder <NUM>. This can provide good axial alignment of the cover <NUM> with the pin <NUM> when installed. The internal shoulder <NUM> may be formed on the internal surface of the rim <NUM>, with the rim <NUM> extending longitudinally past the internal shoulder <NUM> (in a direction away from the cover <NUM>) to the abutment face <NUM>.

The abutment face <NUM> of the retainer <NUM> may extend radially inwardly for abutment not only with the abutment face <NUM> of the rim <NUM>, but also with the rear facing shoulder <NUM>. In such cases, the rim <NUM> preferably extends longitudinally (in a direction away from the cover <NUM>) such that the abutment face <NUM> is aligned with the rear facing shoulder <NUM>.

The circular opening <NUM> of the retainer <NUM> has a radius that is less than the outer diameter of the rear facing shoulder <NUM>.

When both the forward facing shoulder <NUM> and the rear facing shoulder <NUM> are provided, the protector assembly <NUM> may be installed so as to abut the forward facing shoulder <NUM> and the rear facing shoulder <NUM> and thereby prevent axial movement of the protector assembly <NUM> relative to the pipe <NUM>. The abutments with the shoulders <NUM>, <NUM> of the pin can be of sufficient pressure to form seals to hinder or prevent ingress of fluid (e.g. liquid) into the cover <NUM> for thereby protecting the pin <NUM> from corrosion.

As explained above, the cover <NUM> and the retainer <NUM> may define an annular channel therebetween, for example, by virtue of the internal shoulder <NUM> of the cover <NUM> and the radially innermost region of the abutment face <NUM> of the retainer <NUM>. That annular channel of the protector assembly <NUM> can receive a radial extension of the pin <NUM> for relative axial alignment of the pin <NUM> and the protector assembly <NUM>.

In the alternative, or additionally, the pin <NUM> may include a radially extending groove into which a radially extending part of the protector assembly <NUM> may be inserted. For example, the retainer <NUM> may sit within the groove. Once the cover <NUM> is attached to such a retainer <NUM>, the entire protector assembly <NUM> will be locked in an axial position.

The annular channel and/or radially extending part of the protector assembly <NUM> may be located at an axial distance from tapered thread <NUM> and/or complementary thread <NUM>. In particular, the annular channel and/or radially extending part of the protector assembly <NUM> may be located closer to the open end <NUM> of the cover than the tapered thread <NUM> and/or the complementary thread <NUM>.

An embodiment of the protector assembly <NUM> comprising the annular channel and/or radially extending part, wherein the to be protected pipe <NUM> comprises a complementary radial extension or complementary radially extending groove of the pin <NUM>, works in particular well in combination with embodiments having one or more fasteners <NUM>, wherein the head portion(s) <NUM> thereof is/are exposed.

The protector assembly <NUM> may be installed on the pin <NUM> of a threaded pipe <NUM> by a method that includes: covering the pin <NUM> with the cover <NUM>; engaging the pipe body <NUM> with the retainer <NUM>; and fastening the cover <NUM> to the retainer <NUM> with the threaded fastener <NUM>.

The retainer <NUM> may be engaged with the pipe body <NUM> before or after the cover <NUM> covers the pin <NUM>.

Covering the pin <NUM> with the cover <NUM> may involve sliding the cover <NUM> axially over the pin <NUM> and/or threadably engaging the internal coupling thread <NUM> with the thread <NUM> of the pin <NUM>.

Covering the pin <NUM> with the cover <NUM> may comprise abutting the inner surface of the closed end <NUM> with the terminal abutment surface <NUM> and/or abutting the inner shoulder <NUM> with the forward facing shoulder <NUM>.

Engaging the pipe body <NUM> with the retainer <NUM> surrounds the pipe body <NUM> with the opening <NUM> of the retainer <NUM>.

In embodiments in which the retainer <NUM> is a split ring, engaging the pipe body <NUM> with the retainer <NUM> involves deforming the split ring and inserting the pipe body <NUM> between the first and second ends <NUM>, <NUM>. The split ring <NUM> is preferably formed of elastically deformable material so as to revert to its original shape once the pipe body <NUM> has been inserted.

In embodiments in which the retainer <NUM> is a ring assembly, engaging the pipe body <NUM> with the retainer <NUM> involves fastening the first and second parts 200a, 200b together around the pipe body <NUM>. Specifically, the method may involve the step of fastening together the first and second ends <NUM>, <NUM>.

The first and second ends <NUM>, <NUM> are preferably abutted longitudinally (in the direction of the longitudinal axis of the tubular portion <NUM> of the cover <NUM>) and circumferentially (in the direction around the perimeter of the pipe body <NUM>).

The retainer <NUM> and cover <NUM> may be rotationally aligned by insertion of a projection <NUM> of the retainer <NUM> into a notch <NUM> of the cover <NUM>. Alternatively, the retainer <NUM> and cover <NUM> may be rotationally aligned by insertion of a projection of the cover <NUM> (not shown) into a notch of the retainer <NUM>.

Fastening the cover <NUM> to the retainer <NUM> with the threaded fastener <NUM> may comprise engaging the cover <NUM>, the first end <NUM> and the second end <NUM> with the threaded fastener <NUM>. The second end <NUM> may be threadably engaged with the threaded fastener <NUM>. Preferably, both the first and second ends <NUM>, <NUM> are threadably engaged with the threaded fastener <NUM>.

More preferably, the cover <NUM> is not threadably engaged with the threaded fastener <NUM>. However, the fastener <NUM> is provided with a head portion <NUM> that abuts the cover <NUM> to fasten it to the retainer <NUM>.

In embodiments in which a counter bore or counter sink <NUM> is provided in the cover <NUM>, the fastener may be screwed into the bore <NUM> of the retainer <NUM> until the head portion <NUM> is entirely within the counter bore or counter sink <NUM>.

In preferred embodiments, the threaded fastener <NUM> is inserted in the longitudinal direction (in the direction of the longitudinal axis of the tubular portion <NUM> of the cover <NUM>), and is inserted through the rim <NUM> of the cover <NUM> from the side of the closed end <NUM>. In this way, when a plurality of pipes <NUM> are stacked, the operator can carry out the installation of the protector assembly <NUM> from the end of the stack without hindrance by the other pipes <NUM> of the stack.

Preferably, a plurality of fasteners <NUM> are used to secure the cover <NUM> to the retainer <NUM>.

Whereas in the description given above of the preferred embodiment, the retainer <NUM> is either a split-ring or a ring assembly, embodiments are contemplated in which one or more (preferably, at least three) independent retainer(s) 1200a, 1200b, 1200c, 1200d are provided. <FIG> show an example.

In <FIG>, there can be seen a cover <NUM> with a rim <NUM> having a bore through which a fastener 1400a extends. As best seen in <FIG>, the fastener 1400a extends to a retainer 1200a. The fastener 1400a is attached to the retainer 1200a such that they rotate together. As shown in <FIG>, rotation of the retainer 1200a by rotating the fastener 1400a can rotate the retainer 1200a into a first position in which it extends radially inwardly and may engage an external shoulder of a pipe <NUM>, and can rotate the retainer 1200a into a second position in which it does not engage an external shoulder of a pipe <NUM> (shown as 1200a' with dashed lines in <FIG>).

The retainer 1200a may comprise a bore for receiving the fastener 1400a, or the fastener 1400a may engage the surface of the retainer 1200a.

The fastener 1400a preferably has a head portion 1410a for rotational engagement by a tool. That is, a tool (such as a screwdriver or Allen key) may be engaged with the head portion 1410a so that rotation of the tool rotates the fastener 1400a and thereby rotates the associated retainer 1200a between the first and second positions.

As with the fasteners described above, the fastener <NUM> extends through the bore of the rim <NUM> to engage the retainer <NUM>. The fastener <NUM> extends substantially in parallel with the longitudinal axis of the cover <NUM>. The fastener <NUM> is exposed on the cover side of the bore of the rim for engagement by a tool. Alternatively, in some embodiments, the fastener 1400a is exposed such that it may be grasped by a worker and rotated by hand.

Claim 1:
A protector assembly for covering a pin (<NUM>) of a threaded pipe (<NUM>), comprising a cover (<NUM>), a retainer (<NUM>) and at least one fastener (<NUM>) for fastening the retainer (<NUM>) to the cover (<NUM>), wherein:
the cover (<NUM>) includes a tubular portion (<NUM>) defining a longitudinal axis from a closed end (<NUM>) to an open end (<NUM>), the open end (<NUM>) defining a rim (<NUM>) for axial abutment with the retainer (<NUM>);
the retainer (<NUM>) has an abutment face (<NUM>) for abutment with the rim (<NUM>);
the rim (<NUM>) comprises at least one bore (<NUM>) extending therethrough;
a fastener (<NUM>) extends through the bore (<NUM>) of the rim (<NUM>) and engages the retainer (<NUM>), the fastener (<NUM>) extending substantially in parallel with the longitudinal axis and exposed on the cover side of the bore (<NUM>) of the rim (<NUM>) for engagement by a tool or user to operate the fastener (<NUM>),
characterised in that
the fastener (<NUM>) threadably engages with the bore (<NUM>) of the retainer (<NUM>); or
the fastener (1400a) engages the surface of the retainer (1200a).