CA1043142A - Theft resistant threaded fasteners - Google Patents

Abstract

Abstract of the Disclosure A theft resistant threaded fastener wherein the wrenching surface includes a frusto-conical outer peripheral surface and at least three axial slots located around more than 180° of the outer peripheral surface, no two of which are diametrically opposed, each slot having a profile contour, in radial planes, which includes a rounded bottom and straight sides tangent to the bottom and extending to the outer peripheral surface, the sides diverging from one another at an angle of about 120°.

Description

The present invention relates generally to threaded fasteners and pertains, more specifically, to threaded fasteners of the type having a special wrenching configuration constructed to resist their unauthorized removal and theft of the items secured with the fasteners.
The theft of items which, by their nature, are accessible readily to the public has been increasing over the years. Among the most popular items being stolen in large numbers are auto-mobile wheels, including spare wheels, as well as other automo-tive parts, such as batteries, engine components and miscellan-eous accessories. Thieves who are not technically capable of taking an adequately locked car nevertheless rapidly can strip the car of enough parts and accessories to satisfy a need for quickly obtaining smaller amounts of money.
In addition to automobiles, other targets for such theft include part and playground facilities, office equipment, road-way equipment, railroad and other transportation facilities and hotels.
A variety of fasteners has been developed and offered for sale having either key lock mechanisms or special wrenching con-figurations which tend to impede their unauthorized removal.
Key lock mechanisms for fasteners are often bulky and heavy and therefore possess certain aesthetic as well as operational disadvantages. For example, automotive lug nuts, or bolts, employing key lock mechanisms are heavier than plain lug nuts and can unbalance an otherwise balanced wheel. Moreover, such devices are often susceptible to road hazards, dirt, ice and other condi-tions, in addition to tampering, all of which could render the devices inoperative when authorized removal is desired. Addi-tionally, the key locks are easily picked or broken off.

The majority of special wrenching configurations are sus-ceptible to tampering with common tools such as vise grip pliers, : ' ', ~ -.
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punches, chisels and the like. Even if the fastener is not removed with such tools, it is likely to be mutilated to a degree which defeats even authorized removal. Some configura-tions are susceptible to clogging with grease and dirt so that easy authorized removal is not possible. In addition, a great many special configurations are costly to manufacture and re-quire concomitantly expensive tools for their removal.
It is an object of the present invention to provide threaded fasteners having a wrenching configuration which resists unauthorized removal with commonly available tools, but enables authorized removal with ease, utilizing a rela-tively inexpensive special tool.
Another object of the invention is to provide theft resistant fasteners which have a simple, economically manufac-tured configuration which resists mutilation, as well as the deleterious effects of surrounding conditions, to enable easy authorized removal while detering unauthorized removal.
A further object of the invention is to provide a theft resistant fastener configuration which is applicable to a wide variety of fasteners including bolts as well as nuts, and further including cap nuts.
A still further object of the invention is to provide a theft and tamper resistant threaded fastener which is compact and relatively lightweight, thereby rendering the fastener especially well-suited to use as an automotive wheel lug nut or bolt.
According to the present invention there is provided a theft resistant threaded fastener having a thread axis and including a body extending between opposite ends and having a longitudinal axis coaxial with the thread axis, a clamping sur-face on the body adjacent one said end thereof for engaging a workpiece, and an external wrenching surface on the ~04314Z
body, said wrenching surface extending axially from said clamp-ing surface and including an outer peripheral surface which is generally circular in planes perpendicular to said axis and generally frusto-conical in shape tapering with respect to said longitudinal axis between a maximum diameter at a first axial end adjacent the clamping surface and a minimum diameter at a second axial end remote from the clamping surface, and at least three axially extending wrenching slots in the body, each slot being in open communication with and interrupting said outer peripheral surface at the major diameter thereof and having an outwardly concave cylindrical bottom portion, the axis of curvature of said bottom portion being parallel to said longutidinal axis and spaced therefrom a distance greater than one half the diameter of said outer peripheral surface at . the axial location thereof where said slots are of maximum radial depth, said slots being non-uniformly located circum-ferentially from each other around more than 180 of the outer peripheral surface and being spaced from said longitudi-nal axis a distance greater than one half said minimum diameter so that said slots do not interrupt an axial portion of said outer peripheral surface adjacent the second axial end thereof and the total circumferential extent of all of said slots with respect to said longitudinal axis being less than 180~, measured at said axial location of maximum radial depth.
The invention will be more fully understood, while still further objects and advantages will become apparent, in the following detailed description of preferred embodiments illus-trated in the accompanying drawing, in which: .
FIGURE 1 is a top plan view of a threaded fastener in the form of a lug nut constructed in accordanoe with the inven-tion;

.-,, : - ., , , 1043~42 FIGURE 2 is a partial cross-sectional view taken along line 2-2 of FIGURE l;
FIGURE 3 is a top plan view of a threaded fastener in the form of a lug bolt constructed in accordance with the invention;
FIGURE 4 is an elevational view, partially broken away, of the bolt of FIGURE 3;
. FIGURE 5 is a top plan view of a threaded fastener in the form of an alternate lug nut constructed in accordance with ~he invention;

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; .. , ... . , . ,, . . , . .. . . .: -- 1043~42 FIGURE 6 is an elevational view of the nut of FIGURE 5;
FIGURE 7 is a top plan view of a threaded fastener in the form of a cap lug nut constructed in accordance with the inven-tion;
FIGURE 8 is a partial cross-sectional view taken along lines 8-8 of FIGURE 7;
FIGURE 9 is a diagrammatic illustration of the profile contour of a wrencing slot in the above threaded fasteners;
; FIGURE 10 is a top plan view of a tool for wrenching any of the above threaded fasteners;
FIGURE 11 is an elevational view, partially broken away, of the tool; and FIGURE 12 is a bottom plan view of the tool.
Referring now to the drawing, and especially to FIGURES 1 and 2 thereof, a threaded fastener constructed in accordance with the invention is illustrated in the form of a lug nut 20.
Lug nut 20 has a body 22 which extends axially along a longi-tudinal axis A between a first, or upper end 24 and an opposite second, or lower end 26. Body 22 is provided with a threaded aperture 28 for engaging a complementary threaded member in the form of a threaded lug (not shown) in a manner now well known in the mounting of wheels upon automobiles and like vehicles.
Lug nut 20 is provided with a clamping surface 30 adja-cent lower end 26 for engaging a workpiece which, in this in-stance, is the complementary seat (not shown) on an automobile wheel. Since such seats are usually frusto-conical in configur-ation, clamping surface 30 is likewise frusto-conical, tapering from a larger diameter at 32 to a smaller diameter at alower end 26.

A wrenching surface 34 is provided on the body 22 of nut , 1043:~2 20 and enables the nut to be alternately tightened or loosened when placed upon a mating stud. Wrenching surface 34 includes an outer peripheral surface 36 which is frusto-conical in configuration, surface 36 being tapered from a larger diameter at 38, adjacent the clamping surface 30, to a smaller diameter at the upper end 24.
In order to enable the nut 20 to be wrenched, the wrench-ing surface 34 is provided with a plurality of wrenching slots 40 in the body 22 extending axially along the wrenching surface 34. The surface 42 of each slot 40 extends parallel to the : longitudinal axis A of the nut such that corresponding portions of the surfaces 42 of slots 40 are mutually parallel, as well as being aligned parallel with longitudinal axis A. At least three slots 40 are employed and, while more than three can be utilized, three slots are adequate and are preferred.
Turning briefly now to FIGURES 10, 11 and 12, as well as to FIGURES 1 and 2, authorized wrenching of nut 20 is accomplished with a special tool illustrated in the form of tool 50. Tool 50 has a generally tubular body 52 and includes a socket 54 ; 20 at the bottom end 56, socket 54 having an internal configura-tion complementary to the external configuration of the wrench-ing surface 34 of nut 20. Three lobes 58 project radially into the socket 54 at circumferential locations corresponding to the locations of slots 40 in the body 22 of nut 20 and have a configuration complementary to the slots 40.
A standard hexagon wrenching configuration 60 is provided at the upper end 61 of the body 52 of tool 50 so that the tool can be engaged by an ordinary wrench. When tool 50 is placed over nut 20 so that the nut nests properly within the socket 54, ~ ' ' ' , ''~, :

a wrench may be applied to wrenching configuration 60 to turn the nut 20 for the desired wrenching operation.
Attempts at unauthorized wrenching of nut 20, that is, attempts at wrenching nut 20 without a matching tool 50, are resisted by the particular arrangement of the structural elements of the nut. Thus, referring to FIGURE 9, as well as to FIGURES 1 and 2, the slots 40 are each provided with a particular profile contour which, as viewed in radial planes, includes a rounded bottom, illustrated in the form of arcuate bottom 62, and relatively straight sides, shown as straight sides 64. Sides 64 are tangent to arcuate bottom 62 at 66 ; and extend outwardly to outer peripheral surface 36 so that each slot 40 is completely open along the length thereof.
Preferably, the center P of the arc of arcuate bottom 62 is located radially outside of the overall diameter of the outer peripheral surface and the length of the arcuate bottom 62 is confined to an angular extent defined by angles B, measured from both sides of a radial line R. The magnitude , of each angle B is chosen in order to have sides 64 diverge from one another at an angle greater than 90. Preferably, angle B is about 30 so that the sides 64 diverge from one another at an angle of about 120. In this manner, slots 40 provide no significant surface upon which a chisel, punch, pin or a like instrument can gain a purchase sufficient to apply a wrenching torque to unseat a properly seated nut 20.
The impact of such an instrument upon the interior surface 42 of a slot 40 would tend to be directed along a line passing relatively close to longitudinal axis A and, because of a restricted lever arm, would tend to apply very little unseating torque to nut 20. Attempts to redirect such impacts to in-, ' ' ; ~ ' . ' ,: ~ ' ' ., .'. ' ' - .

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crease the lever arm would tend to slide the instrument from the slot. Additionally, the open configuration of slots 40 resists any build-up of dirt, grease and other debris which ; would otherwise tend to prevent the proper nesting and seating of tool 50. Furthermore, the corresponding profile configur-ation of lobes 58 of tool 50 may be modified to depart from the profile configuration of surface 42 of slots 40 to follow more closely the circular outline 68, upon which arcuate bottom 62 lies, thereby providing a clearance space 70 which will accommodate any deformation resulting from mutilation of edges 72 of slots 40 while still enabling proper nesting and seating ; of tool 50 upon wrenching surface 34.
The frusto-conical configuration of the outer peripher-al surface 36 tends to resist gripping of that surface by vise grip pliers or like gripping tools. Such tools will merely tend to slide axially from the nut 20 in the direction toward upper end 24. The angle C made between the outer peripheral surface 36 and longitudinal axis A is great enough to accom-plish the objective of resisting the gripping forces of such gripping tools. However, too large an angle C will tend to increase the overall diameter of the nut, making the nut diffi-'`!, cult to use while increasing the weight of the nut. Smaller ; angles will decrease size and weight, but will provide a greater opportunity for unauthorized gripping tools to take ` hold. It has been found that an optimum magnitude for angle C is about 20. In order to further resist the possibility of such a tool gaining a purchase on the wrenching surface 34, no ; two slots 40 are diametrically opposed; hence, no diametrically opposed axial surfaces are available to be gripped.
In order to further res t gripping by vise grip pliers : .

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and other similar tools, as well as to resist efforts to seat a chisel, punch or other such implement on the wrenching sur- -face 34 of nut 20, the nut preferably is constructed of steel and is hardened to a surface hardness which will attain the desired resistance. Nuts constructed of C-1018 steel and case hardened to a hardness of 60 units on the Rockwell C
scale to a depth of approximately 0.015 inch have exhibited adequate performance. Such a hardness, in combination with the geometric configuration of the wrenching surface 34 renders the nut 20 difficult to mutilate to the point where tool 50 cannot be fitted to the nut.
The tendency for unauthorized tools and implements to tilt out of slots 40 and off wrenching surface 34 is en-hanced by the combination of the frusto-conical configura-tion of outer peripheral surface 36 and the profile contour of slots 40. However, tool 50 will not slip from nut 20 in view of the axial orientation of the internal surface 42 of slots 40 and the positioning of the slots around the periphery of the nut 20. Thus, slots 40 are located around more than 180 of the outer peripheral surface 36; that is, while two adjacent slots 40 may lie along the same 180 arc, the third slot is located outside that arc. However, the positioning of slots 40 relative to one another may be varied from one set of nuts to another. Thus, a purchaser may obtain a set of lug nuts 20 for his automobile and he will be provided with a tool 50 complementary to the nuts of that set. Other sets of nuts would have other locations of slots 40, that is, the angular spacing between slots 40 would vary from the spacing in the first-set, and each set would have its own tool 50.
Hence, one tool 50 would not fit all nuts 20 and a thief could 1~)4314Z
not merely obtain one tool 50 for operating on every set of nuts 20. A very wide range of combinations of slot locations is available so that it would be impractical for a thief to equip himself with tools for all combinations. Moreover, even if equipped with all of the tools for all of the com-binations, a thief would not have available to him the time necessary to match the right tool to the set of nuts before him. Furthermore, by avoiding diametrically opposed slot locations, the availability of a universal tool having merely diametrically opposed lobes is eliminated. In addition, standard twelve-point socket wrenches modified to eliminate some of the points will not be usable with wrenching con-figurations of the present invention where the angular spac-ing between slots is properly chosen to avoid that possibility.
It is noted that since nut 20 has opposite frusto-conical surfaces 30 and 36, a user may attempt to place the nut upon a lug in reverse orientation. However, where slots 40 are not equidistant from one another, tool 50 will not seat properly upon clamping surface 30, but only upon wrench-ing surface 34. Thus, the user will immediately detect a ; reversed nut.
Turning now to FIGURES 3 and 4, another threaded fasten-er constructed in accordance with the invention is illustrated in the form of bolt 120. Bolt 120 has a body 122 including portion 123 which extends axially between an upper end 124 and an opposite lower end 126. Body 122 is provided with a threaded shank 128 for engaging a complementary threaded member in the form of a nut or threaded aperture (not shown).
Bolt 120 is provided with a clamping surface 130 adja-cent lower end 126 for engaging a workpiece which, in this _g_ .
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instance, is a flat surfaced item.
A wrenching surface 134 is provided on the body 122 and enables the bolt to be alternately tightened or loosened when placed in a mating threaded aperture. Wrenching surface 134 includes an outer peripheral surface 136 which is tapered from a larger diameter at 138, adjacent the clamping surface 130, to a smaller diameter at upper end 124.
In order to enable the bolt to be wrenched, the wrenching surface 134 is provided with a plurality of wrench-ing slots 140 which are similar to slots 40 of nut 20 so that bolt 120 can be wrenched with tool 50.
Referring now to FIGURES 5 and 6, another threadedfastener constructed in accordance with the invention is illustrated in the form of lug nut 220. Lug nut 220 is constructed similar to nut 20 in that nut 220 has a body 222 with upper and lower ends 224 and 226, a threaded aperture 228, a frusto-conical clamping surface 230 tapering from a larger diameter at 232 and a wrenching surface 234 with a frusto-conical outer peripheral surface 236 tapering from a larger diameter at 238.
In this instance, however, wrenching surface 234 is provided with a plurality of wrenching slots 240 which differ from slots 40 in that slots 240 terminate adjacent the juxta-posed larger diameters at 232 and 238 at radial shoulders 244.
In this manner, slots 240 do not intersect the clamping surface 230 and thus leave the entire clamping surface 230 intact for bearing against the complementary seat in the wheel to be fastened by lug nuts 220. Additionally, any sharp edges which might occur at the intersection of the slots with the clamping surface are eliminated together with any tendency of lU4314Z
such sharp edges to score the complementary seat. Further-more, proper orientation of the nut on the lug is i~mediately apparent.
Turning now to FIGURES 7 and 8, still another thread-ed fastener constructed in accordance with the invention is illustrated in the form of a cap lug nut 320. Cap lug nut 320 is constructed similar to nut 220 in that nut 320 has a body 322 with upper and lower ends 324 and 326. However, in nut 320, threaded aperture 328 does not pass entirely through the body, but terminates short of upper end 324 to establish a cap at 329. Nut 320, like nut 220, has a frusto-conical clamping surface 330 tapering from a larger diameter at 332 and a wrenching surface 334 with a frusto-conical outer peripheral surface 336 tapering from a larger diameter at 338.
Wrenching surface 334 is provided with a plurality of wrenching slots 340 terminating adjacent the juxtaposed larger diameters at 332 and 338 at radial shoulders 344.
In this instance, however, the frusto-conical configuration is extended upwardly to cover the extended length of nut 320 while still enabling tool 50 to be fitted to the nut.
It is noted that tool 50 is provided with a bore 346 adjacent the upper end 61 which accommodates the extended upward length of nut 320 and enables tool 50 to be seated properly upon the nut.
; It will be seen that the threaded fasteners of the present invention provide a theft resistant wrenching con-figuration which is simple both in manufacture and use, which is exceptionally versatile and which renders the fasteners compact, lightweight and reliable.

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~04;~142 It is to be understood that the above entitled des-cription of embodiments of the invention is provided by way of example only. Various details of design and construction may be modified without departing from the true spirit and scope of the invention as set forth in the appended claims.

Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A theft resistant threaded fastener having a thread axis and including a body extending between opposite ends and having a longitudinal axis coaxial with the thread axis, a clamping surface on the body adjacent one said end thereof for engaging a workpiece, and an external wrenching surface on the body, said wrenching surface extending axially from said clamping surface and including an outer peripheral surface which is generally circular in planes perpendicular to said axis and generally frusto-conical in shape tapering with respect to said longitudinal axis between a maximum diameter at a first axial end adjacent the clamping surface and a minimum diameter at a second axial end remote from the clamping surface, and at least three axially extending wrenching slots in the body, each slot being in open communication with and interrupting said outer peripheral surface of the major diameter thereof and having an outwardly concave cylindrical bottom portion, the axis of curvature of said bottom portion being parallel to said longitudinal axis and spaced therefrom a distance greater than one half the diameter of said outer peripheral surface at the axial location thereof where said slots are of maximum radial depth, said slots being non-uniformly located circumferentially from each other around more than 180° of the outer peripheral surface and being spaced from said longitudinal axis a distance greater than one half said minimum diameter so that said slots do not interrupt an axial portion of said outer peripheral surface adjacent the second axial end thereof and the total circum-ferential extent of all of said slots with respect to said longitudinal axis being less than 180°, measured at said axial location of maximum radial depth.

2. A fastener according to claim 1, wherein there are only three slots.

3. A fastener according to claim 2, wherein said total circumferential extent is at most 120°.