In automobile assembly plants, screwed fasteners are used to join car parts using many techniques. They may be hand-driven, machine driven, or fastened with a combination of hand-insertion followed by tightening by motorised drive, etc. One problem which exists in the automotive industry in relation to the use of screwed fastener systems is failure in a component fastening operation arising from cross- thread and no-start conditions. This problem may be exacerbated when one of the threaded components is retained on the vehicle in a fixed position which is difficult to reach.

Cross-threading occurs mainly due to angular entry of a male fastener into the female component in a situation where the male component is unable to align itself to the hole axis, usually because an operator is holding the male fastener at the wrong angle while rotating it. No-start conditions commonly arise from failure to enter, where the male component is unable to locate the hole in the female component either because the holes in the body parts overlap or the female part is out of alignment with the holes in the body parts, and also due to severe angular entry resulting in the fastener's inability to align itself even to the point of incorrectly engaging cross threadedly.

Such cross-threading and no-start conditions are especially common in situations where the operator has their vision of the position of application obstructed. The

problem results in damage to bolts, screws, nuts and female threads formed on other components, and often requires temporary removal of the vehicle from the assembly line for rectification.

An aim of one aspect of the present invention is to provide a male threaded fastener which overcomes, or at least minimizes, these difficulties in a manner which is superior to existing self-aligning fasteners.

Accordingly, in one aspect the invention provides a fastener comprising: -a head with a shank projecting therefrom, -the shank having a male threaded portion adapted to screw into a corresponding female threaded fastener component, -the threaded portion and shank sharing a main axis extending longitudinally of the shank and a core of desired radius outwardly of which the thread is formed, -the shank having an unthreaded generally cylindrical extension extending coaxially from the threaded portion away from the head and having a substantially circular cross section the radius of which is a near match to said core radius, -the cylindrical extension having a projection extending from its axial end opposite said head, said projection comprised of : -a rounded tip portion offset with respect to said shank axis, and -a transition portion blending between the cylindrical extension and the tip portion.

The projection may have : -a generally hemispherical tip portion having its axis laterally offset with respect to said shank axis, and/or -a transition portion having a generally conical surface blending between the cylindrical extension and the tip portion.

Alternatively the projection may be comprised of : -a ridge extending from said axial end of the cylindrical extension,

-said ridge rising in the direction of the shank axis and continuing around at least part of the periphery of said axial end, -said ridge being contained within the volume subtended by an imaginary axial projection of the cylindrical extension, and -said ridge at least partially surrounding a land area perpendicular to the shank axis.

The lateral offset between the shank axis and the tip axis is preferably between 45% and 55% of the difference between the diameters of the cylindrical extension and the tip portion.

In the assembly of automobiles, the installation of screwed fasteners is achieved most commonly by use of power tools. Many self-aligning fasteners need to be installed in closely confined spaces and, particularly with increasingly compacted arrangements of automotive component assemblies, often there is insufficient space for a conventional socket and universal joint combination driving tool to enable tightening of a fastener. Accordingly an aim of another aspect of the present invention is to provide an improved drive socket configuration and a method of installing threaded fasteners by use of such a configuration incorporating a universal joint which is more compact than existing socket and universal joint combinations, particularly in a direction radial to the axis of rotation.

Any such universal coupling requires a fairly strong degree of self straightening so that when the tool is spun by the power source it does not tilt and throw itself off-axis.

A further aim of said other aspect of the invention is to provide a drive socket configuration whose universal joint remains straight when spun while securely holding a fastener.

Accordingly, in one aspect the invention provides a driving tool for grasping and rotating a threaded fastener being installed by use of a powered wrench having a motor means, wherein the driving tool comprises:

(a) at one end a socket portion adapted to mate with a head of said fastener and having means for retaining said fastener head within the socket portion; (b) an input means adapted to provide drive from the motor means; (c) a connection portion whereby the input means is connected to the socket portion for selectively causing the socket portion to rotate; and (d) within said connection portion the input means provides drive to a universal joint, said universal joint comprising: (i) a cylindrical first joint portion on the input means side; (ii) a universal coupling articulated to transmit the drive from the first joint portion through an angle to a second joint portion which is integrally formed with the socket; (iii) a coil spring surrounding said first and second joint portions and said universal coupling, the spring having an outside diameter no greater than the outside diameter of the socket portion and an inside diameter substantially the same as said first joint portion; and (iv) a sleeve fixed onto the first joint portion to contact an end of the spring and compress it towards the socket.

In another aspect the invention provides a method of installing a threaded fastener into a threaded hole, said fastener comprising a head at one end and a male threaded portion at the other end with said other end having no thread at its tip distal from the head, said method comprising: (a) retaining the head of said fastener within the socket of a driving tool as defined above; (b) rotating said driving tool while pressing the fastener tip into said hole to cause the fastener to align axially with the hole; (c) continuing said rotation to cause the thread on the fastener to engage with the hole; and (d) tightening the fastener into the hole.

Preferably the threaded fastener is a screw or bolt. Preferably the means for retaining said head within the socket comprises a magnet affixed into the base of the socket to

contact the head of the fastener. The fastener tip may be first inserted into the hole while the tool is being rotated or it may be inserted while the tool is not being rotated.

Brief Description of the Drawings In order that the invention in its various aspects may be more fully understood there will now be described, by way of example only, preferred embodiments and other elements of the invention with reference to the accompanying drawings where: Figure 1 is a cross section view of portion of one commonly used prior art screw engaging with a correspondingly threaded nut; Figures 2 to 8 show side views of the points of screws according to various other prior art proposals to overcome the problems described above; Figures 9,10 and 11 show general views of the points of three different screws according to the present invention; Figure 12 is a side view of the screw the tip of which is shown in Figure 11, Figure 13 is an end view of the screw in Figure 12; Figure 14 is an enlarged cross section view of the tip of the screw in Figure 12 ; Figures 15 to 20 show positions of the screw tip from Figure 11 when engaging from various orientations with a nut shown in cross section; Figure 21 is an end view of the tip of a further screw according to the invention with the tip shape indicated by contour lines; Figure 22 is a composite of the cross-section views along planes A-B and B-C indicated on Figure 21; Figures 23 and 24 are respectively an isometric view and a side view of a further screw according to the invention; Figure 25 is an end view in the direction of arrow D shown in Figure 24; Figure 26 is a view of the screw tip in the direction of arrow E shown in Figure 24; Figure 27 is a side view of a driving tool in accordance with one embodiment of the invention; Figure 28 is a cross section through the tool shown in Figure 27;

Figure 29 is a view of one part of the tool shown at right angles to the view in Figure 28 ; Figure 30 is a general view of an alternative, but less preferred, configuration of part of the tool; Figure 31 is a exploded view of the configuration shown in Figure 30; Figure 32 is a cutaway view of a driving tool having a preferred configuration. shown in its unflexed alignment; and Figure 33 is a cutaway view similar to Figure 32 but with the tool shown in its position of maximum flexure.

Detailed Discussion of the Prior Art Figure 1 shows a commonly used form of"dog point"2 on a screw 4 carrying a male thread 5 and engaging with a female threaded nut 6. Automotive fasteners have commonly featured a dog point as a lead-in feature. The cylindrical extension 8 forms a lead-in feature which is pushed into the threaded hole where it is a loose sliding fit. This causes axial alignment of the two threads in order to prevent cross- threading due to misalignment.

The diameter of the extension 8 which forms the dog-point lead-in is important, being slightly larger than the core diameter of the thread 5, but slightly smaller than the inside (minor) diameter of the female thread in the nut 6. If these relationships between the diameters are not properly controlled, relative undersizing of the lead-in can result. While an undersized diameter of the extension 8 would still aid in alignment, it gives rise to cross-threading problems.

The flat end 9 with its sharp edge 10 can make such a dog-point difficult to feed into the hole in the nut 6, particularly if it is not properly aligned angularly as it is led to the hole. This has been addressed to some degree in other prior art configurations shown in Figures 2 to 8.

Figures 2 to 5 show variations of the simple flat-end dog-point which have been marketed. Like features have been identified with like numbers. Figure 2 shows a chamfered edge 12 on the tip, and Figure 3 shows a pointed tip 14. Figure 4 shows a point which uses a generous radius 16 on the periphery of the tip.

Due to space restrictions for the installation of screws employing dog points and their modifications, the length of the cylindrical unthreaded portion of the lead-in is often shortened from the forms shown in Figures 1-4, sometimes to the point of being not very effective for aligning.

Figure 5 shows the Accupoint (trade mark) which features a more bulbous curved tip 18 at the end of an unthreaded neck 20 smaller than the core diameter 22 of the screw thread 5. Our testing has indicated that the present invention is able to provide substantially improved performance when compared with this prior art configuration particularly when engagement is attempted with a nut at relatively high angular entry or relatively high offset entry.

A screw with any of the configurations shown in Figures 1 to 5 can be satisfactorily installed by either pushing it into the nut and then rotating the screw, or rotating the screw as it is pushed in. This is because the main axes of the male and female threads become correctly aligned before the threads can engage. If categorised by the required installation technique, the points shown in Figures 1 to 5 represent a first category of configurations.

A second category of prior art screw ends is illustrated by Figure 6 which shows the so-called U-point. The screw 24 is fully threaded to its tip 26, but the tip has a tapered core 28 carrying the generally fully formed thread. Fasteners in this category have the advantage that the nut does not need to be closely aligned to other holes through which the male component is passed. However a significant disadvantage, when compared with the first category shown in Figures 1 to 5, is that before the screw is rotated, it should be inserted into the nut until the threads engage. Unless this is done, the incidence of cross threading is greatly increased. Accordingly the

screws in this category tend to be used in applications where they are hand fed into position before tightening. In addition, although prior art screw ends in this second category may enable improved entry into threaded holes if the screw and hole axes are parallel but slightly offset, they suffer an increased tendency for cross threading if the axes of the screw and nut have an angular misalignment relative to each other.

A third category of prior art is illustrated by Figures 7 and 8. Screws at these points are designed to be rotated as they are inserted through the holes in sheets and into a mating nut. Figure 7 shows the point described in US Patent No. 4,952,110, and Figure 8 shows an alternative example in the market place. The fasteners in this third category have the advantage that the nut or sheets being fastened can be even further out of alignment than for the screws of the second category. These fasteners utilize an offset or eccentric tip on the screw points 30 and 35. Although the tips each have a flat end face 34 and 38 respectively, the offset allows for a greater search area by the fastener tip in locating holes, as well as the ability to exert a self-aligning force as it turns inside the joint. For the same size thread 5, the end face 34 in Figure 7 has a larger surface than the end face 38 of Figure 8. The point 34 also has discontinuous thread portions 32 on one side of the offset lead-in 33. The tapered portion of point 35 forms portion of a simple eccentric cone 36, while the tapered portion of point 30 has a concave hyperbolic surface 31.

Detailed Description of the Invention Figure 9 shows the point 40 of a screw according to one embodiment of the present invention. The point 40 has a projection 42 forming the lead-in feature which can be considered to have three constituent shapes labelled 46,48 and 56 respectively.

Adjacent the threaded portion of the shank 44, a cylindrical portion 46 extends for a length of approximately 1.5 times its diameter. The diameter of the cylindrical portion 46 is slightly larger than the core diameter of the male thread 5 on the screw, but slightly smaller than the inside (minor) diameter of the female thread in a nut intended to engage the screw in use.

From the circular cross section face 50 at the end of the cylindrical portion 46, the projection reduces in diameter by way of a conical frustum 48. The frustum has two parallel circular faces 50 and 52 in cross section, with one line 54 on the conical surface which joins those faces extending at right angles to the faces. The centre axis 57 of the small face 52 is thus inwards from the edge of the large face 50 by a distance equal to the radius of the small face. From the small face 52 of the frustum there extends an approximately hemispherical protuberance 56 forming a tip portion. The diameter of the face 52 is approximately 30% of the diameter of face 50 so the axis 58 of the threaded portion 44 of the screw does not pass through the protuberance 56.

The presence of this protuberance, when in combination with the tapered reduction in diameter from the cylindrical portion 46, has been found to substantially improve the ability of a screw to align itself in the bore of a nut or other female-threaded device before engaging threads, and thus to substantially reduce the tendency of a screw to cross thread into a nut. The protuberance also improves the ability of the screw to align offset overlapping holes in metal sheets which are being fastened together.

Another embodiment of the present invention is illustrated by Figure 10. The point 60 also has a generally hemispherical protuberance 62 forming a tip portion whose axis 64 is set eccentrically to the axis 66 of the screw. An unthreaded cylindrical portion 68 of the shank extending coaxially from the threaded portion 70 away from the screw head concludes with an oblique end face 72 which is then blended to the circular base of the hemispherical tip portion of protuberance 62 by a cylindrical surface 63. The end face 72 may be generally flat as shown in Figure 10 or may have a gently convex form. The surface 63 joining the hemispherical tip portion of protuberance 62 to the end face 72 may, instead of having the cylindrical form illustrated in Figure 10, have a conical or a hyperbolic surface such that it more smoothly blends the hemispherical tip portion with the end face 72.

A preferred embodiment of the present invention is illustrated by Figure 11. The screw shank 82 carrying a male thread 84 has a point 80 extending to an unthreaded

generally cylindrical extension portion 86 forming a shoulder which is coaxial with the shank 82. The tip 88 has a generally hemispherical form and its axis 90 is laterally offset from the axis 91 of the threaded portion of the shank 82 until the tip 88 just touches the cylindrical portion 86 at a location 93. There is thus a single straight line continuum along the cylindrical portion 86, via the location 93, to the base of the tip 88. Other than on that line, the cylindrical portion 86 is joined to the tip 88 by way of three surface forms linked to, or blended onto, each other. These three surface forms are a concave hyperbolic surface 92 closest the tip, a conical surface 94 and a convex ellipsoidal surface 96 closest the thread 84. Each of surfaces 92,94 and 96 are projected by rotation about the tip axis 90. The boundaries between surfaces 88, 92,94 and 96 are shown by broken lines on Figure 11 although visually those boundaries are indiscernible. The screw point 80 accordingly has a continual smooth flowing surface from the tip 88 to the cylindrical shoulder 86 inclusive, and this has been found to be greatly beneficial in use of the embodiment.

Figures 12 and 13 show a preferred screw embodying the point shown in Figure 11 while Figure 14 shows the point in cross section. Of particular relevance is that: (i) the radius of the surfaces 92 and 94 in profile shown in Figure 14 are in the range of 25% to 75% D (where D is the diameter of the cylindrical portion 86) and preferably in the range 40% to 60% D; (ii) the ratio d/D is in the range 0.25 to 0.45 (where d is the diameter of the tip 88 and D is the diameter of the cylindrical portion 86) and is preferably in the range 0.30 to 0.40; (iii) the lateral offset between axis 90 and axis 91 is (D-d)/2 where D and d are as defined above; (iv) the tip 88 has its leading edge radiused in the range of 40% to 45% d and so leaves a flat leading face 98 of diameter 10% to 20% d on the tip; (v) the length of the cylindrical shoulder 46 is in the range of 25% to 70% of the screw diameter and preferably in the range of 40% to 60%; (vi) the angle of the simple conical surface 94 is in the range of 45° to 65° to the screw axis; and preferably in the range of 50° to 60°; and (vii) the tip is clear of the screw axis 66.

For the preferred embodiment shown in Figures 12 and 14, the tip has a diameter of approximately 33% of the diameter of the cylindrical shoulder portion. Also the screw axis may be laterally offset from the nut axis by a distance of up to 33% of the hole diameter, and the tip will still engage with the hole and lead the screw into the nut.

Figures 15 and 16 illustrate the movement when a screw of the form shown in Figure 12 is brought into engagement with a nut when the screw and nut are axially parallel but offset. In Figure 15, if the screw is pushed into the nut without rotation, this results in the edge of the hole sliding smoothly along the concave portion 92, and conical portion 94, and then convex portion 96 of the point until the cylindrical portion 86 slides neatly into the nut. The screw and nut are then perfectly aligned and their respective threads will engage without the possibility of cross-threading. However if from the position in Figure 15 the screw is rotated, for example by way of a power tool engaged with its head (not shown), as it is pushed into the nut, a different action occurs. As the screw is rotated the tip revolves sweeping out a surface until it engages into the side of the hole. This is the position shown in Figure 15. The screw then rotates for the next half-turn about the axis of the tip until the screw is in a position upside down to that shown in Figure 16, At that stage the axis of the screw is nearly exactly aligned with the axis of the threaded hole, and the unthreaded cylindrical portion of the point can slide into engagement with the nut so ensuring correct alignment of the screw and nut. The nut is formed with a slight countersink 99 to better facilitate the entry of the screw.

As discussed earlier in this specification, the diameter of the cylindrical portion 86 is slightly greater than the core diameter of the thread on the screw but slightly smaller than the inside (minor) diameter of the thread in the nut.

Figure 17 shows the screw entering the nut at a 40° misalignment of the axes. From the position shown, when the screw is rotated and an axial pressure applied to it, the reaction from the rotating tip bearing upon the thread inside the nut causes the screw

to align itself in one turn of the screw to the position shown in Figure 18. The smooth surface, free of sharp edges, on the tip is beneficial in preventing damage to the nut's thread during this operation.

Figure 19 shows the screw entering the nut at a 30° misalignment of the axes. This time the screw is not being rotated and entry is facilitated by the countersunk leading edge of the nut sliding along the surfaces 92,94 and 96 until the tip contacts the nut's thread well within the nut. Subsequent rotation and axial force on the screw will bring it into full axial alignment upon a full turn of the screw. Alternatively, if from the position shown in Figure 19 the screw is rotated as it is pushed along its axis into the nut, the screw will rise to about the same position shown in Figure 17 and then twist into axial alignment as discussed above with reference to Figures 17 and 18.

From the above discussions with reference to Figures 11 to 20, it can be seen that the screw shown in Figure 12 performs exceptionally well in applications where the screw is inserted into the nut either while rotating the screw or before starting to rotate it, where the screw is fed to the nut in a substantially off-centre manner, and where the axis of the screw has a substantial axial misalignment with the nut.

The screw point 100 shown in Figures 21 and 22 has a significantly different form to that of the above described embodiments of the invention. The tip extending from the axial end 103 of the unthreaded cylindrical extension portion 102 takes the form of a ridge 104 which rises in the direction of the shank axis 105 and continues around approximately two thirds of the periphery of the circular axial end of the cylindrical portion 102.

The tip illustrated is adapted for use on a right hand threaded screw and the ridge rises along a leading ridge line 110 to a peak 106 and then falls along a trailing ridge line 111 to its base at the end 103 of the cylindrical portion 102. The leading ridge line 110 with its outer flank 108 is the main interacting surface on the tip when the screw is inserted into a mating threaded hole of a nut at an angle to the hole's axis. The outer flank 108 of the ridge continues the form of the cylindrical portion and is thus

largely perpendicular to the end 103 except for a rounded extremity. The outer flank 108 does not extend radially out beyond an imaginary axial projection of the cylindrical extension.

The inner flank 109 of the ridge slopes to a land area 112 on the plane of the axial end 103. This embodiment of the invention is particularly adapted for forming in a forging operation as the flat land area 112 is useful for engagement by a push out pin in the forging die. The circular dashed line in Figure 21 indicates the extent of the engagement of such a push out pin and its centre at 113 is offset relative to the shank axis 105.

The point of the screw 120 shown in Figures 23 to 26 is similar to that of Figures 21 and 22, varying only in the shape and positioning of the ridge 126 forming the tip.

The shank 122 has a cylindrical extension portion 124 with an axial end 125 containing a land area 134. The land area is for the most part bounded by the ridge 126 with its peak 128 forming the extremity of the tip. In this embodiment the outer flank 130 is a generally cylindrical surface co-extensive with the extension portion 124 and the inner flank 131 is also a generally cylindrical surface coaxial with the outer flank 130. The leading ridge line 132 rises very steeply and is almost axial in direction whereas the trailing ridge line 133 falls away in a more gradual manner after an initial steep portion 135 near the peak 128.

The positioning of the land area 134 in this embodiment allows a push out pin in a forging die to press against the screw point at a more axially central location on the end 125 when compared with the screw of Figures 21 and 22. The smooth rounded surface 136 formed on the ridge line, and especially on the leading ridge line 132, allows the tip to contact a thread inside a nut and, when rotated, force the screw into axial alignment with the nut without damaging the thread in the nut.

The above description refers to screw portions or constituent shapes being"joined"by some means. A screw is usually formed as a unitary item from a single piece of metal, and the dissection of its form into components for the purposes of the above

explanation does not indicate separate component manufacture followed by joining.

The screws described would preferably be formed from a single piece of metal wire or rod by forging, rolling, and/or turning operations.

In order to optimise the installation of screws incorporating self-aligning points as described above, driving tools have been developed for use with rotary power tools.

One embodiment of such a driving tool will now be described with reference to Figures 27 to 29, another embodiment described with reference to Figures 30 and 31, and a preferred embodiment described with reference to Figures 32 and 33.

Referring to Figures 27 and 28, a driving tool 210 comprises a socket portion 212 at one end connected by a connection portion shown generally as 214 to a drive input shank 216. The socket portion 212 has a hexagonal socket recess 218 appropriately sized to receive the hexagonal heads of fasteners which are to be installed using the tool. At the bottom of the socket recess 218 a ring shaped magnet 220 is securely fixed into a smaller recess. The magnet firmly holds the head of steel fasteners mated into the socket recess 218 so that the fasteners are not expelled when the driving tool is rotated by the motor. The flat exposed face 219 of the magnet stands slightly proud of the face 217 of the recess and is perpendicular to the main axis of the socket recess 218 so that a flat topped head of a fastener securely contacts and is held against the flat face 219 of the magnet so holding the fastener firmly axially aligned with the socket. In this way the fastener is held more securely than if it was supported simply by the peripheral walls 215 of the recess 218 which necessarily have a significant clearance from the head of the fastener.

The input shank 216 has a hexagonal cross-section looking along its main axis so that it is able to firmly engage with the chuck of a powered driving tool (not shown in drawings). The shank 216 butts onto a cupped portion 222 which forms a cylindrical first joint portion of a universal coupling 223. The socket portion 212 is integrally formed with a ball-like extension 226 which forms a second joint portion of the universal coupling 223.

The cupped joint portion 222 carries a spherically-bottomed recess 228 into which the ball 226 locates. A cylindrical pin 230 passes, with an interference fit, through the side walls of portion 222 and, with a neat fit, diametrically through the ball 226 via a bore 232. As can be seen from Figures 28 and 29, the bore 232 is elongated to slots 233 at the surface of the ball 222 but bore 232 is tapered inwards towards the centre from each side of the ball so that the bore has a circular cross section 231 at the centre. Accordingly the universal joint has an angular freedom of movement between the ball 226 and the recess 228 in the plane of the Figure 28 cross section due to movement of the pin through the slot, and movement in the axial plane of the coupling at right angles to the Figure 28 cross section due to rotation of the ball 226 about the pin's axis, but no freedom of movement in the axial direction of the tool 210. The ends of the pin 230 lie flush with the outside diameter of the cup portion 222.

A coil spring 234 surrounds the universal coupling, being at one end supported by the outside of the cupped portion 222 and at the other end by a circumferential recess 236 on the socket portion. During assembly of the tool 210, the ball 226 is placed in the recess 228 and the pin 230 inserted to lock portions 222 and 224 together. The spring 234 is then placed onto the assembly from the input shank end, sliding it over the neatly fitting cupped portion 222 and locating the leading end onto the step 236, and a sleeve 238 is fitted neatly onto the outside of the cupped portion 222 to compress the spring somewhat before the sleeve 238 is then locked to the cupped portion 222 by means of grub screws, pins, welding or other suitable means.

The sleeve 238 has the same outside diameter as the socket portion 212 and the same or slightly larger outside diameter than the spring 234. By configuring the universal coupling in this way, the outside diameter of the spring 234 is kept below the outside diameter of the socket portion 212 while still providing a spring which provides the required axially self-centering action for the universal coupling and also providing a means for assembling the complete tool 210.

The depth of the socket recess 218 is preferably slightly less than the depth of the heads of the bolts or screws to be installed. In this way the rim 242 of the socket portion 212 does not contact the substrate material during installation operations, thus avoiding damage of the substrate. The reduced depth of the recess 218 also serves to reduce the dimension of the tool from the universal's central pivot pint 240 (midway along the axis of pin 230) to the rim 242.

An alternative to the above-described"pinned ball and cup"configuration of universal coupling is shown in Figures 30 and 31. Each end of the coupling 250 has a yoke 252,253 and these are pivotally linked by pins 256,257 and an offset connector 259. The construction and operation of this coupling 250 is apparent from Figures 30 and 31. Other alternative universal coupling configurations may be used, while still ensuring that it be sufficiently compact to be contained within the inside diameter of the coil spring 234 while the outside diameter of the spring is no greater than the outside diameter of the socket portion 212.

Referring to Figures 32 and 33, a driving tool 310 comprises a socket portion 312 at one end connected by a connection portion shown generally as 314 to a driver input socket portion 316. The socket portion 312 has a hexagonal socket recess 318 appropriately sized to receive the hexagonal heads of fasteners which are to be installed using the tool. At the bottom of the socket recess 318 a disc shaped magnet (not shown) is securely fixed into a smaller recess 320. The magnet firmly holds the head of steel fasteners mated into the socket recess 318 so that the fasteners are not expelled when the driving tool is rotated by the motor. The flat exposed face of the magnet stands slightly proud of the face 317 at the bottom of the recess 318 and is perpendicular to the main axis of the socket recess 318 so that a flat topped head of a fastener securely contacts and is held against the magnet so holding the fastener firmly axially aligned with the socket. In this way the fastener is held more securely than if it was supported simply by the peripheral walls 315 of the recess 318 which necessarily have a significant clearance from the head of the fastener.

The driver input socket portion 316 has a socket 321 having a square cross-section looking along its main axis so that it is able to firmly engage with a square ended shaft of a powered driving tool (not shown in drawings).

The connection portion 314 has a bearing 322 comprising steel balls 324 captive between a cylindrical inner bearing surface 326 and a cage 328. The inner bearing surface 326 is rigidly connected to, and shares its axis 327 with the socket portion 312. The balls 324 bear also against a cylindrical outer bearing surface 330 which is rigidly connected via an outer casing 332 to the driver input socket 316. The outer bearing surface 330 shares its axis 331 with the driver input socket 316.

The cage 328 forms a part-spherical shell and has slotted apertures through which the balls protrude. There are an even number of balls 324 in the assembly, preferably eight. Each ball runs in a rounded groove let into the inner bearing surface 326 and at the same time runs in another rounded groove let into the outer bearing surface 330.

Each of these two grooves are set at opposite angles to their respective bearing axes 327 and 331. Adjacent grooves in each surface are set at opposite angles to their neighbours. By this means the bearing surfaces can move so that the axes 327 and 331 can tilt relative to each other as shown in Figure 33, while at the same time the bearing surfaces cannot rotate about their axes 327 and 331 relative to each other and the joint cannot be readily pulled apart. Universal couplings of this general type are well known in automotive transmission systems but their adaptation in this modified form for installing fasteners has been previously unknown.

The cage when tilted bears against the head of a piston 334 which slides in the bore of the outer casing 332. The piston is biased by a preloaded spring 336 towards the cage 328 so that there is a significant reaction load from the piston against the cage when tilted and this load tends to straighten up the connection portion 314 and thus align the axes 327 and 331. Instead of using the spring 336, the piston may be biased by other compression means such as pressurised gas, an elastomer plug or other suitable means.

A rubber boot 338 spanning between the socket portion 312 and the outer casing 332 protects the bearing and piston surfaces from foreign materials. When the tool 310 is flexed to avoid an obstruction, the boot 338 is drawn inwards on the side closest the obstruction and thus more easily avoids the obstruction.

Those skilled in the art will appreciate that the invention in all its aspects as described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications which fall within its spirit and scope.

Examples of such variations include: (a) Instead of the hexagonal cross-sectioned shank 216 as shown in Figures 27 and 28, an input shank may be used which has a square or circular cross section. The circular alternative may have flats formed on its end (eg. a hexagonal end) in order to more securely engage a chuck or other grasping means on the powered driving tool.

(b) The input shank 216 may be replaced by a socket, preferably square (like socket 321 shown in Figure 32) or hexagonal, let into the cup portion 222 with the socket engaging a mating shaft extending from the motor means. A tool configuration with a socket at its input end is generally less preferred than the shanked version described with reference to Figures 27 and 28 because the fixed shank provides greater rigidity and less uncontrolled movement than a socket with a separate shaft.

It will be also understood that where the word"comprise", and variations such as "comprises"and"comprising", are used in this specification, unless the context requires otherwise such use is intended to imply the inclusion of a stated feature or features but is not to be taken as excluding the presence of other feature or features.