GB2169978A

GB2169978A - Safety fastening

Info

Publication number: GB2169978A
Application number: GB08501484A
Authority: GB
Inventors: Derek Valentine Hall
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-01-21
Filing date: 1985-01-21
Publication date: 1986-07-23
Also published as: GB2169978B; GB8501484D0

Abstract

A screwthreaded fastening, that is to say a threaded nut or a threaded bolt or screw. So that the fastening cannot easily be mischievously unfastened, the nut or the head of the bolt or screw, is of generally frusto-conical form with a helical groove (12) extending some way around its frusto-conical surface and opening from the smaller end of the frusto-conical surface for the connection of an extraneous tool including a driving peg or member capable of engaging the groove. <IMAGE>

Description

SPECIFICATION Safety fastening The invention relates to a safety fastening, that is to say to a fastening which can be used when building a structure which might be prone to terrorist attack or which might possibly be subject to criminal damage or vandalism or theft.

Structural steel constructions which could in certain circumstances be expected to be prone to terrorist attack include bridges and the various joints and fastenings along railway tracks, including the rail mountings, signalling installations and the like.

Hitherto, it has been all too easy to destroy or interfere with such structures and installations simply be slackening or removal of the conventional screwthreaded fastenings with which they have been built. Similarly, secure areas for the storage of fuel, weapons, computer systems and the like have been able to be broken into relatively easily if conventional screwthreaded fastenings have been accessible so that they have been able to be slackened or removed.

The object of the invention is to provide a screwthreaded fastening which will provide at least some measure of protection against mischievous unfastening.

According to the invention, there is provided a screwthreaded fastening, that is to say either a nut or a head of a bolt or screw, which is of generally frusto-conical form with a helical groove extending some way around its frusto-conical surface and opening from the small diameter end of the frustoconical surface for the connection of an extraneous tool including a driving peg capable of engaging said groove, the "hand" of the helix of the groove being such that the extraneous tool can be used to turn the fastening in a direction to tighten it.Preferably, the included angle of taper of the frusto-conical surface of the fastening will be between 30 and 1200 and preferably in the region of 40". The helix angle of the groove may be between 5 and 45" and preferably in the region of 15".

In order that the invention may be fully understood and readily carried into effect, the same will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a perspective view of a nut embodying the invention, Figure2 is a longitudinal section through the nut on the line 2-2 in Figure ian extraneous tool for tightening the nut being shown in chain-dotted lines, Figure 3 is a view similar to Figure 1, of a bolt embodying the invention, and Figures 4 and 5 are views similar to Figures 1 and 3 which illustrate possible variations of the nut and of the bolt respectively.

Referring now to Figures 1 and 2 of the drawings, the nutthere illustrated has a right hand thread 10 and is of generally frusto-conical form, as shown, with a helical groove 12 extending some way around the frusto-conical surface 14. (The groove is termed as helical groove because of the fact that the basal surface of the groove is at a constant radial distance from the axis of the nut, even though at the surface 14 it describes a spiral). The groove opens from the smaller diameter end of the frusto-conical surface for the connection of an extraneous tool shown in chain-dotted lines in Figure 2. As shown, the ex traneoustool includes a driving peg 16 capable of engaging the helical groove of the nut and of drawing a frusto-conical shaped depression surface 18 of the tool into engagement with the similarly shaped surface of the nut.

As previously stated, the nut illustrated has a right hand thread. Consequently, it will be seen that the "hand" of the helix of the groove is such that the extraneous tool can be used to turn the nut in a direction to tighten it. Any attempt to slacken the nut by the use of the extraneous tool illustrated will simply result in the driving peg sliding along the groove and tending to push the tool away from the fastening. It is vertually impossible to slacken the nut by any normal means once it has been fully tightened. Any jaw-type tool designed to grip the external surface of such a nut will simply slip off its frustoconical surface.Consequently, it will be understood that the nut is very useful for the building of structural steel constructions which could in certain circumstances be expected to be prone to terrorist attack, for example structural steel bridges and the various joints and fastenings along railway tracks including the rail mountings, signalling installations and the like. Similarly the nut can be used for the building of enclosure structures for creating secure areas for the storage of fuel, weapons, computer systems and the like. The use of the nut described will not make it absolutely impossible to slacken or remove the fastening of which it forms a part, but its use will make it so much more difficult to do so that it will be substantial safeguard against terrorist attack or criminal interference or against mindless vandalism.

It will of course be understood that the invention is not only applicable to a nut but can equally well be embodied in a bolt or screw. In Figure 3 there is illustrated a bolt with a head 20 which is of exactly the same shape as the nut of Figures 1 and 2 and which can be engaged by the same extraneous tool for tightening. The bolt illustrated has a right hand thread.

It will of course be understood that if the nut or bolt or screw concerned is to have a left hand thread, the helical groove will have a left handed helix also, as illustrated in Figures 4 and 5 respectively. It will also be understood that the fastenings may have any desired thread form.

It is possible that a relatively large nut or bolt head could have more than one helical groove for the engagement of an extraneous fastening tool having the same number of driving pegs. However, the nut illustrated, which had a 318" diameter screwthread, had only a single groove because it was thought that the cutting of two such grooves could weaken the nut too much. (Of course, the same size bolt could probably be provided with a pair of oppositely disposed helical grooves because it has a solid head).

Although the extraneous fastening tool illustrated in chain-dotted lines in Figure 2 is a box-key type of tool with a tommy bar it will be understood that this is merely byway of simple illustration andthatthe tool could be of various forms. It may for example be formed in the manner of a conventional ring key.It could in fact be formed in the manner of an open ended spanner, the gap between the jaws of the spanner being a clearance fit over the threads of the screw or bolt concerned so that, in effect, the frusto-conical shaped depression surface of the spanner capable of engaging the similarly shaped surface of the nut concerned extends around slightly more than half of the periphery of the nut It will be understood that by trial and experiment it will be possible to determine the optimum angles for the taper of the frusto-conical surface of the nut or of the head of the screw or bolt, as the case may be, and for the helix angle of the groove. It may be found that, ideally, these angles should vary according to the size of the nut, bolt or screw concerned. It may also be found that if the nut or the head of the bolt or screw, as the case may be, is provided with two or more helical grooves to that the tightening torque is equally balanced, the included angle of taper of the head can be made somewhat greater, for example 60 instead of 40 .

Claims

1. A screwthreaded fastening, that is to say either a nut or head of a bolt or screw, which is of generally frusto-conical form with a helical groove extending some way around its frusto-conical surface and opening from the smaller diameter end of the frusto-conical surface for the connection of an extraneous tool including a driving peg capable of engaging said groove, the "hand" of the helix of the groove being such that the extraneous tool can be used to turn the fastening in a direction to tighten it.

2. A screwthreaded fastening according to claim 1, in which the included angle of taper of the frusto-conical surface of the fastening is between 30 and 120

3. A screwthreaded fastening according to claim 2, in which the included angle of taper of the frusto-conical surface of the fastening is in the region of 40 .

4. A screwthreaded fastening according to any one of the preceding claims, in which the helix angle of the groove is between 5" and 45 .

5. A screwthreaded fastening according to claim 4, in which the helix angle of the groove is in the region of 15 .

6. A screwthreaded fastening shaped and adapted to be used substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.