Combination torque release screw and screw driver

A threaded fastener adapted to be threaded into a workpiece only to a predetermined torque is provided which includes a pair of frangible lugs mounted on the fastener head and engageable by a specialized driving tool. The tool is used to initially engage the lugs to partially spread the latter apart and frictionally couple the driver and fastener so as to facilitate insertion of the fastener; when the fastener is fully threaded into the workpiece, excess torque applied through the driver causes the lugs to cleanly break off from the head, thus presenting a tamper-proof connection. The lugs can be mounted directly on the fastener head or on an annular mounting element frangibly secured to the head itself. The tool includes a head of generally circular cross section having a pair of radially outwardly extending cam projections which engage the fastener lugs during driving operations. In preferred forms, the tool also includes respective, planar lug-engaging faces which ensure that the fastener lugs are cleanly separated from the fastener at the completion of the driving operation.

This invention relates to a specialized screwtype fastener which is adapted 
to be threaded into a workpiece to a desired, predetermined torque level, 
and to a specialized driving tool to be used in conjunction with the 
fastener. More particularly, it is concerned with such a fastener and 
driver combination wherein the fastener is provided with a pair of spaced, 
frangibly secured lugs which are adapted to break from the fastener head 
when excess torque is applied; the tool on the other hand includes a head 
of generally circular cross section having outermost cam-like projections 
which engage the fastener lugs and serve to cleanly break the latter off 
from the head when the fastener is fully embedded into a workpiece. 
Various types of torque release screws have been proposed in the past. In 
general, these types of fasteners are designed to be installed into a 
workpiece or the like, but are provided with structure for ensuring that 
the fastener can only be tightened to a desired, predetermined torque. 
Exemplary torque release fasteners are illustrated in U.S. Pat. Nos. 
1,506,500, 2,830,635, 3,673,912 and 3,854,372. 
It is the most important object of the present invention to provide an 
improved, simplified screw fastener which is adapted to be threaded into a 
workpiece or the like only up to a predetermined torque, and which is 
incapable of further tightening after the desired torque limit has been 
reached. 
As a corollary to the foregoing, another object of the invention is to 
provide a screw fastener which includes an elongated, threaded shank 
having a head and at least a pair of spaced lugs frangibly coupled to the 
head; the lugs have a break-off resistance correlated with the 
predetermined torque value of the fastener, in order that the lugs can 
break free of the fastener head when a torque is applied which is greater 
than the predetermined desired torque. 
Another object of the invention is to provide a screw fastener of the type 
described wherein the break-off lugs are in spaced relationship in order 
to receive a driving tool therebetween such that the tool can engage the 
lugs and initially spread the latter apart to a limited degree so as to 
establish a frictional engagement between the tool and fastener lugs; in 
this manner the fastener can be screwed into the workpiece, and, when the 
fastener is fully embedded, torque applied through the tool serves to 
cleanly break the lugs free from the fastener. 
A still further object of the invention is to provide a specialized driving 
tool for use with the threaded fasteners hereof which includes a handle, a 
shank secured to the handle, and a driving head secured to the shank, with 
the head being of generally circular cross section and including a pair of 
spaced, radially extending cam projections adapted to engage corresponding 
lugs on the threaded fastener. The tool also includes a generally planar, 
radially outwardly extending face adjacent the outermost end of each cam 
projection in order to provide direct, face-to-face engagement between the 
respective faces and the corresponding fastener lugs.

Referring now to the drawing, a threaded, torque release fastener 10 is 
illustrated in FIGS. 1-6. Fastener 10 includes an elongated, threaded 
shank 12 having an enlarged, integral, frustoconical head 14. Head 14 
includes a central opening or recess 16 which is important for purposes to 
be described, along with a pair of opposed, upstanding lugs 18 which are 
secured to the generally planar uppermost face 20 of the head 14. As best 
seen in FIGS. 1-4, the lugs 18 are preferably located adjacent the 
periphery of face 20 and extend inwardly therefrom, and are spaced 
180.degree. apart on head 14. The lugs 18 are secured to face 20 along 
respective lines of weakness or frangibility 22. As will be more fully 
described hereinafter, the connection between the lugs 18 and head 14 is 
correlated with the desired predetermined torque level for the overall 
fastener 10. 
A driving tool 24 is also illustrated in FIG. 1 and includes a handle 26, a 
shank 28 secured to the handle, and a radially enlarged driving head 30 at 
the end of shank 28 remote from handle 26. Head 30 is of generally 
circular cross section (see the dotted circular representation, FIG. 3), 
but includes a pair of circumferentially spaced, radially extending 
projections 32 which present respective outer cam surfaces adapted to 
engage the innermost upstanding edges of the respective lugs 18. In 
addition, the head 30 is configured to present a generally planar, 
radially outwardly extending face 34 adjacent the outermost end of each of 
the projections 32. The faces 34 are disposed to face in opposite 
directions relative to one another and are located 180.degree. apart on 
head 30. Moreover, the faces 34 are configured to abut, in a face-to-face 
relationship, the lugs 18 during the driving of fastener 10. It will also 
be noted that the bottommost surface of head 30 is provided with a 
central, axially extending projection 35 which is adapted to be received 
within the opening 16 within fastener head 14. 
In use when it is desired to install the fastener 10 into a workpiece 36, 
the following occurs. First, the user places head 30 of tool 24 between 
the lugs 18. This initial positioning is facilitated by provision of the 
cooperating projection 35 and opening 16. That is to say, the user first 
aligns the head 30 with the fastener head 14 and inserts projection 35 
into opening 16. The user then grips the fastener 10 and rotates tool 24 
in a clockwise direction until the cam-projections 32 on head 30 first 
begin to engage the inner edges of the respective lugs 18. This causes the 
lugs 18 to spread apart in a radial direction relative to the axis of 
fastener 10 to a limited degree, and thereby establishes a frictional 
connection between the head 30 and the fastener. This is advantageous in 
that the fastener is in effect coupled to the tool 24 for more convenient 
driving, especially in hard to reach places. In any event, the user then 
begins to thread fastener 10 into workpiece 36, and this action continues 
in the normal manner until the fastener is essentially completely embedded 
within the workpiece. At this point continued rotation of tool 24 causes 
the faces 34 of head 30 to come into full and complete engagement with the 
corresponding lugs 18 (see FIG. 4), and continued application of torque 
through tool 24 then causes the lugs 18 to be broken off completely from 
head 14. When this is accomplished, no further driving of fastener 10 is 
possible. 
It will be readily understood that the lugs 18 are connected to fastener 
head 14 along respective lines of weakness which are correlated to the 
desired predetermined torque level for the fastener. That is to say, in 
the design of fastener 10 the lugs are secured in a manner such that they 
will break cleanly from head 14 when a predetermined torque level is 
reached. 
Another fastener 38 in accordance with the invention is illustrated in 
FIGS. 8-11. Fastener 38 includes an elongated, threaded shank 40, an 
integral, frustoconical head 42, and a central opening 44 in the head. In 
this case however, an annular circumscribing mounting element or ring 46 
is frangibly coupled to the periphery of head 42 along a single, 
continuous line of weakness or frangibility 48. A pair of opposed, 
circumferentially spaced lugs 50 are in turn secured to the annular 
element 46. A driving tool having a head 52 is provided for use in 
conjunction with fastener 38, with the head 52 being in all respects 
similar to head 30, save for the fact that it is of somewhat larger radial 
dimensions. Specifically, the head 52 includes a pair of outwardly 
extending projections 54 presenting cam surfaces, along with a pair of 
radially outwardly extending, opposed faces 56. 
During driving operations with screw fastener 38, the same general 
procedure is followed as in the case of fastener 10 and tool 24. 
Specifically, the tool head 52 is first placed between the respective lugs 
50 and rotated until the cam projections 54 come into engagement with the 
inner edges of the latter. The fastener 38 is then threaded into the 
workpiece 36 until the fastener is essentially completely embedded. At 
this point continued application of torque through the tool head 52 causes 
a break-off of the entire annular ring 46 along the annular line of 
frangibility 48. This condition is illustrated in FIG. 10. Just as in the 
case of fastener 10, when the element 46 (and of course lugs 50 connected 
thereto) break free of the fastener head, no further tightening of the 
fastener 38 is possible, and the user knows that the fastener is tightened 
to the predetermined, desired torque level.