FRICTION MECHANISM

TECHNICAL FIELD

This invention relates to a friction mechanism.

Specifically, the present invention relates to friction mechanisms which are variations on fastener mechanisms.

BACKGROUND ART

The present invention relates particularly to fastener mechanisms such as bolts and screws.

For ease of general reference both bolts and screws are understood to include a head and a threaded shaft. Bolts tend to differ from screws in that bolts tend to have an even cross-section throughout the shaft (excluding the effect of the threads) whereas screws tend to be tapered to a point at the end of the shaft distal to the head. As can be appreciated there are many thousands of variations on bolts and screws and the principles of the present invention can be applied to many of these.

It should be appreciated that the fastener industry is internationally estimated at being worth US$40 billion per annum.

One of the disadvantages with bolts as used presently is that it is estimated that approximately 50% of mechanical failures occur as a consequence of nuts and bolts shaking loose.

An extreme example of such failures is the crash of a Concorde at Charles De Gaulle Airport in Paris. This occurred because a small metal strip fell off a DC10 plane onto the runway.

There have been numerous attempts and many patents filed which discuss the efforts of parties around the world to invent a fastening mechanism in the form of a bolt that strongly secures elements together but does not shake loose with vibration.

Some of these mechanisms include:

In the most basic form a simple threaded bolt and nut pair are used, with very careful control of the tightening process. If the correct rotational force is applied this can be reliable, but the correct force is very hard to apply, measure or check. Common wisdom in the fastener industry is that the correct axial stretch of the bolt when best tensioned (usually by the nut) is 0.5 to 1.0% of the lineal stretch. The problem with this method is the additional time, equipment, skill and expense, required to achieve the desired forces.

Standard spring or split washers attempt to provide an axial operating force creating a bias of one thread against the other. Unfortunately the split washer is completely compressed in use, and therefore largely acts as a standard flat washer, with a small anti rotation benefit only if the leading edges of the split area are sharp.

Loctite™ is an anaerobic glue which can be effective in binding threads but is very sensitive to cleanliness and temperature, somewhat messy to use, requires a close tolerance between the cooperating elements

Using a pair of threaded nuts is a strategy used sometimes. This improves the vibration resistance but is cumbersome slow and adds expense. Additionally it only improves vibration resistance a little as the axial stretch of the fastener still determines the efficacy of the thread friction engagement (now on two nuts).

Castle nuts are used where the shank of the bolt is pierced, and a pin is able to pass through both a pair of castellations on the nut, and the hole in the bolt shank, thereby avoiding rotation or the castle nut. This improves the vibration resistance but is cumbersome slow and adds expense.

Patent number DE 10204721 discloses a spring bolt which enables the length of the fastener to change. This has a helical spring which extends from the head of the bolt and connects to a solid threaded region. This only has a small threaded portion at the end thereof joined to the non threaded flexible spring. This device does not have the strength of even conventional bolts.

Patent number JP 2005/325,999 discloses a fastening mechanism a first fastening member having a vibration source to a second fastening member. This is a means to dampen vibrations, not to provide a strong secure fastening. Again it only has a small threaded portion which is attached to a spring.

Patent number PCT/IL2001/00924 discloses an interested fastening mechanism which has a variable pitch thread configuration. This consists of a split threaded cylinder which in its resting states has threads substantially parallel to each other. Twisting the cylinder in the appropriate direction creates either a right hand or a left hand thread. The cylinder is not fixed to a head as such and as a consequence of the split along its length provides a flexible, but not very strong fastening device.

Patent number US 4,917,554 discloses a corkscrew like fastener used to join together semi-rigid mats. This consists of a head and shaft wound from circular wire in the form of a helix. While this is useful with amorphous products such as mats, this can not be used where structural strength is required. The round wire of the 'corkscrew' cannot readily cooperate with a solid object nor provide the strength, grip or fine tolerances that a simple threaded bolt can.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinence of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein; this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising ¹ is used in relation to one or more steps in a method or process.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF INVENTION

According to one aspect of the present invention there is provided a fastening mechanism including

a head

a shaft fixed to one end of the head wherein

at least part of the shaft is effectively threaded, and

at least part of the shaft has no anchoring base for the thread,

the fastening mechanism characterised in that

the shaft and thread are formed from at least one unbroken wound spiral.

It is envisaged that the principles behind the fastening mechanism of the present invention can be used in a variety of situations. For ease of reference however the fastening mechanism shall be referred to as a bolt or screw. It should be appreciated however that this is not intending to be limiting.

Also, it should be appreciated that the present invention could cooperate with complementary threads (such as in a nut) or directly into a material.

The head of the present invention can be of any shape or configuration required for the bolt to be "done up" or "undone". For example, the head may be hexagonal with sides of a shape and size designed to cooperate with standard spanners and the like.

In other embodiments, the head may be designed to cooperate with various screw drivers, such as chisel or flat head or Philips head.

In other embodiments the head may have a recess which is designed to cooperate with the end of an Allen key.

The main purpose of the head is to provide something for the shaft to fit onto and the user to rotate with the appropriate tools for the situation.

The shaft likewise can be any length or thickness suitable for the particular application in which it is intended to be used.

In most embodiments however it is envisaged that the shaft will be substantially straight and abut the head at substantially right angles thereto. While this should not be seen as limiting, it should be appreciated that this is a standard configuration used for most bolts and screws, being the most practical.

The term "effectively threaded" should become more apparent in the following descriptions of the construction of the shaft. However, the aim of the present invention is to be able to provide a bolt or screw which has external threads able to cooperate with either complementary threads or materials in a similar manner to existing bolts and screws. Generically, a thread in the present invention is a spiral ridge extending along the shaft wherein the threads themselves are non-circular in cross-section.

In preferred embodiments the threads are of a fairly conventional form with a sharp or tapered edge which can readily cooperate with complimentary threads in the same means as a conventional bolt and nut. It is this interaction that gives requisite strength, grip, fine tolerances and required interaction between the two objects.

With a conventional bolt or screw the shaft is a solid piece of material into which a spiral ridge or thread has been cut. This configuration means that the length and

diameter of the shaft remains substantially constant when in use as there is no flexure, compression, or extension provided for in this design.

This means that for a bolt to cooperate with a nut, the fit between the complementary threads has to be loose enough to allow the nut and bolt to be readily done up with respect to each other, yet tight enough to ensure that vibration of the bolt does not cause the nut to shake loose. As discussed previously this is a significant problem with the prior art.

Meeting these requirements and the very fine tolerances required is understandably very difficult.

With the present invention, the threads of the bolts are not cut into a solid shaft as with the prior art. The inventor has deduced that the solid shaft in the prior art acts as an anchoring base for the threads which gives this inflexibility of movement.

In preferred embodiments of the present invention the threads themselves actually form the shaft of the fastening mechanism.

Thus, preferred embodiments of the present invention have the thread and shaft formed as consequence of a spiral wound from the head of the fastening mechanism. This spiral can flex, compress or extend according to the forces placed on the shaft as there is no anchoring base to resist these.

It should be noted that the shaft and thread are formed as one from at least one unbroken round spiral. This means that there is at least a 360° turn to form the shaft and thread. Naturally in preferred embodiments there are many such turns.

This is in contrast with PCT Patent Application No. PCT/IL2001/00924 which has a slot cut along the length thereof making that piece of prior art insufficiently strong for the desired uses of the present invention.

It should be appreciated that it is envisaged that the material from which the shaft may be made (which could be different from that of the head) is preferably of a type and construction that possess a material "memory". This means that if the shaft is deformed through forces placed on it, there is a natural tendency for the material "memory" to bias the shaft back towards its original shape.

Thus in use, a bolt in accordance with the present invention can have a shaft which has threads in a normal position at the same or slightly greater outer diameter than that of the nut into which the bolt is to be threaded. The action of screwing the bolt into the nut can cause the shaft of the bolt to compress under the pressure of this action. This is possible because there is no central core to resist the compression. However, once the screwing action has stopped, the natural memory of the material from which the shaft is made (in combination with the spiral form) causes the shaft to extend outwards in an attempt to resume its original shape. It is this action that causes the threads of the bolt to form a far closer friction fit with the threads of the nut and thereby provide resistance to vibration - unlike the prior art.

Likewise, to remove the bolt from the nut requires a screwing action which again will cause the shaft to compress making it easy to remove.

It should be appreciated that in alternative embodiments the shaft may be partially, or include a portion which is solid, as for a conventional screw.

However it should be noted that in preferred embodiments the shaft and thread are one which gives the required structural strength in comparison to the spring bolts discussed in the Background Art Section of the specification.

The solid portion may be a central core around which the spiral shaft is positioned. Alternatively it may be a portion of the length of the screw, for example a portion of the length adjacent to the head may be solid.

This invention describes a hybrid fastener, with self locking detail, which for example may be partially a conventional fastener with a solid core, and partly a fastener which is without a solid core, or any other detail as described in this specification.

The torsional forces from the screwing action cause the pitch and thread spacing of the shaft to alter and conform to the complementary thread with which it is being used.

The torsional forces from the screwing action cause the pitch and thread spacing of the shaft to alter and conform to the complementary thread with which it is being used. If the pitches and or thread detail are different then relative rotation will cause friction which leads to elastic deformation of one or both parts. This will apply particularly to the externally threaded part as it has no solid core at least part way in its axial length, and as such is better able to elastically deform (lengthen or shorten depending on the details of the two parts).

Generally in the embodiments herein described for at least part of the fastener axial length the pitch detail differs form the pitch detail of the cooperating part and this creates a controlled mismatch of the parts. When the two parts engage there is a requirement that one or both parts compress or stretch to align the threads and allow continued rotation.

In comparison it has been found that a conventional spring will not work as a self locking spring thread fastener if its thread is in frictional resistance with the female thread, as the simple action of turning the fastener thread causes the spring helix to unwind and become larger in diameter, thereby stopping further progress.

The present invention has a structural thread, and is thread capable of resisting expansion in diameter but accommodating the pitch mismatch by axial stretching.

In comparison a simple spring detail will bind and be able to rotate no more. The structural thread is the non solid helical core

Thus it can be appreciated that the torsional action of screwing and unscrewing the bolt compresses the shaft providing a product which is easy to undo or do up. However, any vibrational forces subsequently resulting are easily resisted by the bolt and nut combination as a consequence of the memory of the shaft pushing the threads out against the internal threads of the nut.

It should be appreciated that the term nut is only used as one example. The action of the present invention can be used to screw into other materials, whether threaded or unthreaded. However, the basic principles remain the same in that the torsional screwing action can cause the shaft to compress and the vibration forces are resisted as a consequence of the friction fit caused by the memory of the shaft material causing it too bear against whatever it screws into.

Reference to the present invention should now be made to it being a spring bolt, as you can see from the following description that this term can cover a wide variety of embodiments.

One variation of the present invention should now be referred to as a helical bolt. Please note that these principles can also apply to screws and rivets.

In one embodiment of the present invention the helical bolt is formed with a traditional head such as that used in other bolts. The shaft however is effectively an evolution of a standard shaft if one could imagine the threads cut so deep into a standard shaft that there is no effective central anchoring core with regard to same.

Another way of considering the configuration of the helical bolt in accordance with the present invention is to imagine a flat spring spiral whereby the outer edges of

the spiral have approximately the same spacing with respect to each other as do the threads on a conventional bolt. One end of the spiral is attached to a conventional head.

Means by which such a helical bolt can be formed are varied.

In one embodiment, the shaft may be helically extruded. Other embodiments may include injection molding, lost wax casting, machining, and removal of stock. Depending on the method of manufacture the shaft may be made separately or together with the head. Preferably the two are formed integrally as this will provide a far stronger fastener than otherwise.

A different embodiment of the present invention will now be referred to as a hollow form expandable bolt.

This embodiment still has the general principle of there being no anchoring base for the threads of the bolt.

It is envisaged that the hollow form expandable bolt will be used where maximum strength and vibration resistance is required.

This differs from the helical bolt in that the hollow form bolt has an aperture which passes through the head and along the shaft of the bolt. A solid inner plug can be fitted into that aperture.

In use the hollow form bolt is screwed into position with the threads deforming appropriately during the screwing action as described previously. Once the bolt is in place, the internal plug can then be pushed, or screwed, into the central aperture thus providing resistance against the compression of the threads by the external nut or other materials.

It should be appreciated that in this particular embodiment the plug enhances or may even replace the requirement of the memory of the shaft material.

To remove the bolt, it may be unscrewed with the plug in place, although it is envisaged that there is provided a means by which the plug can be readily pulled, or unscrewed, therefrom allowing the bolt to be unscrewed.

It is envisaged that in preferred embodiments the expandable bolt will be finely threaded for the particular applications in which it is envisaged to be used.

These threads can be in some embodiments positioned on the shaft in groupings. For example, there may be a five thread spiral with gaps between each group of five threads. This form should be referred to as a multiple point helix, or a multiple start helix. This variation can be used on all types of embodiments of the present invention, and is not intended to be restricted to just the expandable bolt version.

The internal aperture of the bolt may come in many forms. In one embodiment the internal aperture may have sides which are parallel to the outside of the bolt forming a substantially straight cylindrical hole therethrough.

In preferred embodiments however the central aperture is tapered through the length of the shaft.

In some embodiments the uses of the helical plug, the central aperture could be filled with a buffering or lubricating material.

The plug or insert that can be pushed into the aperture may also come in a variety of forms. For example the insert may in some embodiments be threaded itself. In other embodiments the insert may be another bolt. It could In some embodiments be a wedge or taper or multiple objects.

When an insert is retained with in the hollow form, or expandable, bolt aperture the insert expands the bolt creating a fuller engagement of the threads. However there is also created a reactionary force from the expanded hollow form, which holds the insert via enhanced friction.

The embodiment described could be an improvement alternative to a Rawl ™ bolt, a common masonry anchor fastener used in the construction industry where a threaded bolt element engages into a two or more expandable elements, and by rotation of the threaded element, there occurs radial separation of these elements, and they bind on the substrate, commonly concrete or rock.

The embodiment described in this invention could be expandable but would require only a single expandable element and therefore offer cost and convenience savings, relative to the prior art.

In some embodiments, the aperture could serve as a passageway for substances to pass therethrough or be a means by which a further attachment can be connected to the bolt.

In particular, this would be suitable for fixing holes in concrete or inserting into plastic, metal or other material, rather than necessarily into a threaded element such as a nut.

Yet another embodiment of the present invention is one which shall be referred to as a helical expanded plug.

This embodiment has particular use as a concrete expansion plug or for fixing a hole into other materials such as wood, plastic and metal.

In this embodiment, there is a central aperture that runs through the shaft as does the hollow form expandable bolt. However, the threads in this version are very coarse and in preferred embodiments are formed by the off-axis twisting of a strip

of material that forms the shaft.

In this embodiment, the purpose of the threads is in most cases not to cooperate with complementary threads, but to supply sufficient flexibility to the shaft so that an internal plug (perhaps similar to that used in expandable bolt) can be placed into the aperture of the expandable plug causing the plug to expand outwards and be secured in position.

There is a problem in the aeronautic area with shearing of fasteners just below the head. The underling cause of this is vibration of the aircraft, but specifically the cause is the vibratory wearing action of the sharp edge of the hole drilled in the secured panel work (commonly aluminium, stainless, or titanium, or their alloys). The vibration leads to wear and weakening of the fastener, but it has been found that if the fastener outer diameter is the same or even slightly greater than the drilled hole in the panel work then the shear problem is greatly reduced.

Presently, where rivets are used the fastener expands to form a secure fit into the drilled hole, but there are many applications here a riveted fastener is not desirable, for example where panels need to be removed for inspection for corrosion damage).

What is needed is a fastener that is removable, but also offers the expandable character of the rivet, to better deal with vibration and shearing issues. This invention describes a fastener that meets these requirements being with a hollow core and being expandable in outer shank diameter when used.

One means by which the expandable plug can be secured in place is to effectively compress the plug into the material, the act of compressing causing the external diameter of the plug to increase and hold it into place. This is a similar action to that used with pop rivets, but made more achievable with the present invention due to its ability to be up-scaled by the use of the threads and the greater

compression/expansion achievable by having the threads.

Referring to the previously described hollow form, the insert could pass through the proximal (head) end, and then through the entire length of the of the hollow form, and extend beyond the end, and be attached to a threaded nut, at this distal end, so that turning the insert and or the nut, would compress and shorten the hollow form outer part, and expand its outer diameter.

Alternatively the previously described hollow form the insert could pass through the proximal (head) end, and into a threaded part of the distal end of the hollow form. In this case turning the threaded insert into the threaded distal part, would compress and shorten the hollow form outer part, and expand its outer diameter.

Effectively, the inner plug engages with a distal element to alter the external dimensions of the outer part of the mechanism.

Yet another embodiment of the present invention will be referred to as a wrap form helical fastener.

This embodiment is in the form of a self locking screw or bolt.

As with the previous embodiments of the present invention, this does not have an anchoring base for the threads as such. However, this embodiment differs from the others in that the threads are caused by the overlapping of the material that forms the shaft. For example, the shaft could be envisaged as being made from a long strip of material which has been wrapped in spiral form with the edges of the strip forming threads or barbs.

It is envisaged that this embodiment of the present invention can come in either screw or bolt form depending on whether the natural tapering end of the screw prepared by the process is retained or not.

In this embodiment there is provided tension against the threads as a consequence of the spiral wrap being contained within the shaft of the screw.

It is envisaged that applications of this particular embodiment would be similar to that used for the helical bolt.

According to a further embodiment of the present invention there is provided a method of manufacturing a fastening mechanism as previously described characterised by the following steps:

a) forming at least part of a shaft from a preformed expanded helix, and

b) compressing the helix to create by shortening the linear length thereof to create the final form of the shaft.

In some embodiments, the head of the fastening mechanism is attached to the one end of the shaft prior to compression of the helix, or even prior to the initial production of the helix from the shaft material. However, the inventor envisages that the contact surface of the top of the helical shaft with the head would be less than that achieved in a preferred embodiment of the present invention whereby the shaft is attached to the head after compression.

Other embodiments of the present invention can be formed by extrusion, wrapping, rotation casting, forging and other means, particularly if the present invention lies on a relatively compressed form helix to create same.

It can be seen that the present invention and all of its embodiments provides significant advantages over prior art.

There is provided a means by which a fastening mechanism can be readily used as a consequence of its flexible properties conferred by the lack of an anchoring base for its threads.

This allows the fastening mechanism to be readily inserted or screwed into position or out of same.

However, the configuration of fastening mechanism is such that any non-torsional force meets with considerable frictional resistance of the threads against the material or nut into which the fastening mechanism is screwed.

It should also be apparent that the simplicity of design of the present invention means that the fastener mechanisms can be relatively easily manufactured using known techniques.

It can also be seen that the present invention can be provided in the form of a kitset including a threaded aperture (as part of another object such as a nut) in addition to the fastening mechanism where the threaded aperture can cooperate with the threads on the fastening mechanism. In some embodiments there may be a pitch mismatch between the aperture and the mechanism. And in other embodiments the kitsets may also include inner plugs as previously described.

BRIEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from the ensuing description which is given by way of example only and with reference to the accompanying drawings in which:

Figure 1 is a side view of a helical bolt in accordance with one embodiment of the present invention, and

Figure 2A & B illustrate cross-sections of a hollow form expandable bolt in accordance with the present invention, and

Figure 3A & B illustrate a further embodiment of a hollow form expandable bolt in accordance with the present invention, and

Figure 4A & B illustrate a helical plug in accordance with one embodiment of the present invention, and

Figure 5A & B illustrates a wrap form helical screw in accordance with the present invention, and

Figure 6A, B & C illustrates a generic spring bolt in accordance with the present invention cooperating with the threaded aperture in a nut, and

Figure 7 illustrates a hollow form expandable bolt which includes an extended insert.

BEST MODES FOR CARRYING OUT THE INVENTION

Figure 1 illustrates a helical bolt generally indicated by arrow (1) in accordance with one embodiment of the present invention.

The helical bolt (1) has a head (2) which is hexagonal in cross-section and of a size and shape similar to that of known bolts.

Attached to the head (2) is a shaft generally indicated by arrow (3) having threads (4).

Unlike conventional bolts, the bolt (1) does not have a solid shaft which acts as an anchoring base for the threads. Instead, the bolt (1) has the threads (4) form the shaft itself. This is achieved by having a substantially flat helical spiral, the outer edges of which forms the threads (4).

It can be seen clearly from the drawing that it is possible for the length of the shaft (3) to extend or compress if appropriate forces are placed on same. Extending the

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shaft (3) will cause a reduction in the diameter of the threads (4) and an increased spacing between the threads (4). This most likely will occur when a torsional force is placed on the bolt (1) when it is being screwed into another threaded member such as a nut (not shown). However the inherent memory of the material from which the shaft (3) is made in combination with the strength of the material and the helical form means that once the bolt (1) has been screwed into position the threads (4) will try to bias to their original diameter and spacing. This can cause a friction fit with the threads of the nut and thus make a combination resistant to loosening through vibration.

Another embodiment of the present invention is illustrated in Figures 2A and 2B. Figure 2A is a cross-section of the hollow form expandable bolt (5) illustrated in Figure 2B.

The bolt (5) has a hexagonal head (6) to which is attached a shaft generally indicated by arrow (7).

Again, the shaft is formed by the threads (8) of the bolt (5). In this embodiment, the threads are very fine and grouped together in a strand which is wrapped helically to form the shaft.

In this embodiment, the bolt (5) has a hollow aperture (9) passing through the head (6) and the shaft (7). This hollow aperture (9) in the embodiment shown is tapered and able to receive inserts within the form of plugs, wedges or liquids.

Figures 3A and 3B illustrate another variation of the hollow form expandable bolt this time generally indicated by arrow (10).

In this embodiment the head (11) is circular in cross-section. The shaft generally indicated by arrow (12) has less fine threads (13) than those illustrated in Figures 2A and 2B. In this embodiment the threads are still grouped together but have a

significant aperture gap (14) between the groupings.

The bolt (10) also has a central aperture (15) which passes through the head (11) and the shaft (12). However, in this embodiment the aperture (15) is of constant cross-section and not tapered.

Figures 4A and 4B illustrate a helical plug generally indicated by arrow (16) which is suitable for inserting into material such as concrete.

The plug (16) has a head (17) which is circular in cross-section.

The shaft generally indicated by arrow (18) is formed from the threads (19) which arise out of twisting a thick strip of material not only around in the helix, but also tilting the material with respect to the central axis of the plug (16). The plug (16) also has a central aperture (20) which passes through the shaft (18) and the head (17).

Figure 5A illustrates a wrap form helical screw generally indicated by arrow (21). Figure 5B is a cross-section of the shaft generally indicated by arrow (22) of the screw (21).

The screw (21) has a head (23) which has a central aperture (24) of shape and size to accommodate an Allen key.

The shaft (22) of the screw (21) is formed by wrapping material into a tight spiral generally indicated by arrow (25). The threads (26) on the shaft (22) are formed by the overlapping edges of the wrapped material.

It can be seen that all of the previous embodiments do not have an anchoring base as such for the threads and therefore the threads are capable of movement with respect to each other dependent upon the forces being placed on same. Yet, the construction of the fastening mechanisms in accordance with the present

embodiment is such that the innate memory of the material causes the threads to be biased back to their natural position once in place, thus resisting vibrational forces.

Figure 6 illustrates a generic spring bolt in accordance with the present invention generally indicated by arrow (30). This shows how the shaft (31) of the spring bolts in general can interact with threaded apertures (not clearly shown) such as those contained with articles like a nut (32).

This also shows how a bolt can be manufactured with a head (33) through compressing the shaft (31) before attachment to the head (33).

Figure 7 illustrates a hollow form expandable bolt generally indicated by arrow (40) which includes a head (41 ), shaft (42) and an extended insert (43). The extended insert (43) passes through the entire length of the bolt (40) and attaches to a nut (44).

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.