Screwdriver bit for phillips-head fasteners

Abstract

 A modified Phillips-type screwdriver bit is disclosed that is fully compatible with a standard Phillips-head fastener, and is designed to significantly increase the level of torque that can be applied to the fastener while at the same time substantially reducing the cam-out forces normally produced by a standard Phillips screwdriver-bit. These results are accomplished by the use of a driver having a cross-shaped recess formed in the head thereof, and having associated therewith an axis and including a bit portion symmetrical about any plane containing the axis of the driver and adapted for insertion into said recess which comprises radially symmetrical wing means having generated side surfaces and defining roots therebetween for rotationally driving said fastener on said side surfaces in the same manner in both rotational directions. Preferably said wing means comprise four equally radially spaced bit wings defined by generated side surfaces that in turn define an included angle between adjoining bit wings that progressively increases from a first predetermined angle at the base of said bit wings to a second greater predetermined angle at an axially spaced distance therefrom. The radially outwardly facing surfaces of said bit wings may be tapered toward a common point at an angle relative to the axis of said bit portion substantially equal to the Phillips-standard wing angle. The roots of said bit portion are preferably oriented relative to said bit axis at an angle substantially equal to the Phillips-standard root angle.

Description

[0001] The present invention relates to screwdriver bits and in particular to an improved screwdriver bit for Phillips-head fasteners that significantly reduces the "cam-out" experienced with conventional screwdriver bit for Phillips-head fasteners.

[0002] Conventional Phillips-head fasteners and screw-drivers were originally developed to provide a fastening system that would facilitate efficient installation of fasteners on an assembly line. In particular, as compared to conventional slotted screws, the Phillips screw was designed to centre quickly and easily on the screwdriver and permit more torque to be applied to the screw so that it would hold tighter than conventional slotted screws. In addition, it was expressly contemplated that, when applied by automated screwdrivers on an assembly line, the increasing torque applied to the Phillips screw would eventually cause the drive to pop out of the recess in the screw. In other words, the original Phillips-head design was intended to cause cam-out of the driver without damaging the screw head. It is, of course, this tendency of the Phillips-head design to cause cam-out of the driver, that is a principal source of irritation for craftsmen and ordinary consumers alike.

[0003] It is, therefore, the primary object of the present invention to provide an improved screwdriver bit that satisfies standard Phillips-head geometry and, therefore, is usable with standard Phillips-head fasteners and yet is designed to significantly reduce the tendency of the driver to cam-out of the recess in the screw head. In addition, it is an object of the present invention to provide an improved driver for Phillips-head screws that enables the application of significantly greater torque loads to a standard Phillips-head screw with minimum distortion of the shape of the recess in the screw head.

[0004] Furthermore, it is an object of the present invention to provide an improved driver for Phillips-head screws that enables the application of significantly greater torque loads to a standard Phillips-head screw equally in both rotational directions.

[0005] US-A-2 046 838 discloses a non-Phillips standard driver for non-standard Phillips fasteners having a cross-shaped recess formed symmetrical about any plane containing the axis of the driver and in the head thereof, the driver having associated therewith an axis and including a bit portion adapted for insertion into said recess. The bit wings in the disclosed driver are described as having flat side surfaces.

[0006] FR-A-2 469 250 is directed to a Phillips standard driver provided with an enlarged base portion that is integrally formed with bit wings or ribs for added structural integrity. The lateral faces or side surfaces of the bit wings are described as being planar.

[0007] According to the present invention, we provide a driver for a standard Phillips-head fastener having a cross-shaped recess formed in the head thereof, the driver having associated therewith an axis and including a bit portion symmetrical about any plane containing the axis of the driver and adapted for insertion into said recess characterised in that it comprises radially symmetrical wing means having generated side surfaces and defining roots therebetween for rotationally driving said fastener on said side surfaces in the same manner in both rotational directions.

[0008] Preferably said wing means comprise four equally radially spaced bit wings defined by generated side surfaces that in turn define an included angle between adjoining bit wings that progressively increases from a first predetermine angle at the base of said bit wings to a second greater predetermined angle at an axially spaced distance therefrom. The radially outwardly facing surfaces of said bit wings are preferably tapered toward a common point at an angle relative to the axis of said bit portion substantially equal to the Philips-standard wing angle. The roots of said bit portion are oriented relative to said bit axis at an angle substantially equal to the Phillips-standard root angle.

[0009] In a preferred driver, a gap is formed between said radially outward facing surfaces of said bit wings and the opposing outer radial surfaces of said recess when said bit portion is fully inserted into said recess. A gap may be formed between the root areas of said bit portion and the opposing surfaces of said recess when said bit portion is inserted into said recess, and the base of said bit portion may be truncated.

[0010] Preferably said wing means are adapted to rotationally drive said fastener in both rotational directions initially adjacent said roots and progressively radially outward therefrom along said side surfaces as torque levels applied by said driver to said fastener increase. In a preferred driver said wing means initially engage said recess and drives said fastener along lines of contact adjacent and substantially parallel to said roots.

[0011] Further according to the invention, we provide a driver for a standard Phillips-head fastener having a cross-shaped recess formed in the head thereof defining recess wings having outer radial surfaces that are tapered toward a common point at a predefined standard wing angle relative to the axis of the fastener the side surfaces of adjoining recess wings defining a predefined standard included angle that remains substantially constant from the bottom of said recess to the top of said recess and wherein the sidewalls of said recess wings are oriented at a predefined standard root angle relative to said axis such that the thickness of said recess wings expands in the axial direction from the bottom of the recess to the top of the recess; said driver including a bit portion adapted for insertion into said recess comprising: four bit wings having radially outward facing surfaces that are tapered toward a common point at an angle substantially equal to said standard wing angle relative to the axis of said bit portion and wherein the thickness of said bit wings adjacent the roots of said bit wings increases gradually in the axial direction at an angle approximately equal to said standard root angle but remains substantially constant along said tapered radially outward facing surfaces, and further wherein said generated side surfaces of said bit wings define an included angle in a plane substantially normal to said bit portion axis that progressively changes in the axial direction from a first angle adjacent the base of said bit wings to a second different angle adjacent the radially outer tips of said bit wings. Preferably said bit wings define roots therebetween that are oriented relative to the axis of said bit at an angle substantially equal to said standard root angle.

[0012] In one preferred embodiment, said bit is adapted to engage said recess when said bit portion is inserted into said recess at the generated side surfaces of said bit wings along lines of contact adjacent and substantially parallel to said roots. The area of engagement between the recess and said bit portion may expand progressively radially outwardly from said lines of contact as the torque levels applied by said driver to said fastener increase. A gap may be formed between said radially outward facing surfaces of said bit wings and said opposing outer radial surfaces of said recess wings when said bit portion is fully inserted into said recess.

[0013] In a preferred driver, a gap may be formed radially inward from said lines of contact between the roots of said bit portion and the opposing surfaces of said recess when said bit portion is fully inserted into said recess. The base of said bit portion may be truncated.

[0014] Preferably said bit wings are radially symmetrical such that equal levels of torque can be applied from said driver to the fastener in both rotational directions by all four bit wings.

[0015] In order that the invention may be better understood, preferred embodiments will now be described in greater detail by way of example with reference to the accompanying drawings in which:-

Figure 1 is a side elevational view of a standard screwdriver bit for Phillips-head screws;

Figure 2 is an end view of the Phillips bit shown in Figure 1;

Figure 3 is a sectional view taken along line 3-3 in Figure 2;

Figure 4 is a partial sectional view taken along line 4-4 in Figure 3;

Figures 5 - 11 comprise a progressive series of sectional views of a standard Phillips-type bit and screw fastening system starting from the base of the wings of the screwdriver bit in Figure 5 to the top of the head of the fastener in Figure 11;

Figure 12 is a side elevational view partially in section of a standard Phillips fastening system; Figure 13 is a force vector diagram illustrating the cam-out force component generated by the standard Phillips fastener system;

Figure 14 is a sectional view of a standard Phillips fastener system illustrating the deformation of the recess in the head of the fastener;

Figure 15 is an enlarged view of one of the outer radial wing sections shown in Figure 14;

Figure 16 is a side elevational view of a Phillips-type screwdriver bit according to the present invention;

Figure 17 is a simplified perspective view of the bottom end of the bit shown in Figure 16;

Figures 18 - 24 comprise a progressive series of sectional views of the Phillips-type fastening system according to the present invention from the base of the wings of the screwdriver bit in Figure 18 to the top of the head of the fastener in Figure 24;

Figure 25 is an enlarged view of one of the wing sections of the Phillips-type fastening system according to the present invention;

Figure 26 is a sectional view similar to Figure 24 showing the screwdriver bit applying maximum torque to the fasten;

Figure 27 is a side elevational view partially in section of the Phillips-type fastening system according to the present invention;

Figure 28 is a force vector diagram illustrating the cam-out force component generated by the Phillips-type fastener system according tot he present invention; and

Figure 29 is an enlarged side elevational view partially in section of one of the wing sections of the Phillips-type fastening system according to the present invention.

[0016] The structure, significance, and advantages of the present invention are believed best understood if described in relation to a standard Phillips screwdriver bit. Accordingly, Figure 1 in the drawings illustrates a standard No.2 Phillips bit 10 and will be used as a starting point for the description of the present invention. A standard Phillips bit 10 has a cross-shaped tip that is formed through the creation of four wedge-shaped concave recesses that converge toward the tip 11 of the bit. The recesses define four evenly spaced wings 12 that are tapered along their outer radial surfaces 14 toward the tip of the bit. The angle of this taper is referred to as the "wing angle" and in a standard No.1, 2 or 3 Phillips bit is equal to 26 degrees 30 minutes relative to the vertical axis of the bit. The radially innermost part 16 of each recess is referred to as the "root" 16 and the angle at which the root diverges from the tip relative to the axis of the bit is referred to as the "root angle". In a standard No.2 Phillips bit, the root angle of that portion of the bit 10 adapted to engage the fastener is 5 degrees 45 minutes, as shown in Figure 3. The root angle in a standard No.3 Phillips bit is also 5 degrees 45 minutes; however, the root angle is 7 degrees in a standard No.1 Phillips bit. In addition, as best illustrated in Figure 4, the angle formed by the adjoining interior wing surfaces 18, referred to as the "included angle", is 92 degrees in a standard No.1, 2 or 3 Phillips bit and remains constant along the entire axial length of the bit wings 12. Finally, the tip 11 of the standard Phillips bit is conically shaped as shown in Figure 1 to form a point, the conical surface diverging from the point at an angle of 19 degrees relative to the plane normal to the axis of the bit. The specifications and dimensions for standard Phillips-type bits are defined in literature published by the Screw Research Association.

[0017] Given the above geometry for a standard Phillips bit 10, it is important to bear in mind, as shown in Figures 5-11, that the cross-shaped recess 20 formed in the had 22 of a standard Phillips-head fastener 24 is created with a punch having precisely the same dimensional characteristics. Accordingly, the standard Phillips screwdriver bit 10 is adapted to fit precisely into the recess 20 formed in the head 22 of a standard Phillips fastener 24, except for a designed-in tolerance clearance which enables the bit to fit readily into the recess 20. This relationship is clearly demonstrated in Figures 5 - 11 which comprise sectional views of a standard Phillips-type fastening system progressing in the axial direction from the base of the bit wings 12 in Figure 5 to the top of the head 22 of the fastener 24 in Figure 11.

[0018] In view of the precise conformity between the driver 10 and the recess 20 in the head 22 of the fastener in a standard Phillips-type fastening system it will be appreciated that as the screwdriver bit 10 is rotated in the clockwise direction, torque is applied to the head 22 of the fastener 24 along the outer radial edges 18 of the bit wings 12, as indicated by the arrows appearing in Figures 5 - 11. This occurs due to the simple geometric fact that the points farthest from the centre of rotation move the greatest distance. Therefore, assuming a substantially uniform tolerance gap between the bit 10 and the recess 20, the outer radial edges 18 of the bit wings 12 ill take up the tolerance gap first and engage the opposing outer recess wing surfaces, establishing lines of contact there along. The concentration of torque along the outer radial edges 18 of the bit wings 12 results in the recess wings 21 in the head 22 of the fastener 24 deforming in these areas as torque levels increase. This deformation is illustrated in somewhat exaggerated form in Figures 14 and 15. Once this deformation occurs, the radially outward facing end surfaces 14 of the bit wings 12 come into contact with the newly formed opposing surfaces 26 in the deformation areas, thereby generating a significant force in the vertical direction (i.e. out of the paper relative to Figures 14 and 15) causing the driver 10 to "cam out" of the screw-head recess 20.

[0019] This phenomenon is illustrated and the related force vectors diagrammed in Figures 12 and 13. In particular, as the torque applied along the outer radial edges 18 (Figure 11) of the bit wings 12 increases and deformation of the outer radial areas of the recess wings 21 occur, a force is generated by the radially outward facing end surfaces 14 of the bit wings 12 against the deformed surfaces 26 of the recess wings 21 in a direction normal to the end surfaces 14, as indicated by the arrows 27 in Figure 12. This, in turn, creates an equal and opposite force from the deformed surfaces 26 against the radially outward wing surfaces 14. This opposing force, designated "Z" in the force diagram illustrated in Figure 13 is comprised of a horizontal force component, designated "X", and a vertical force component, designated "Y", generated by the application of torque from the screwdriver bit 10 to the fastener 24 is equal to a factor of 0.43 (i.e. sin 26 degrees 30') times the magnitude of the force vector "Z". In other words, the greater the application of torque, the greater the force tending to cam the screwdriver bit 10 out of the recess 20 in the head 22 of the fastener 24.

[0020] To obviate this cam-out tendency of the standard Phillips fastening system, the improved Phillips-type screwdriver bit according to the present invention has been designed so that torque loading between the bit and the recess in the head of a standard Phillips fastener is confined to the side faces of the bit wings. This is accomplished in the manner described below. Referring now to Figures 16 and 17, an improved Phillips-type screwdriver bit 30 according to the present invention is shown. At the outset it is important to note that the present screwdriver bit 30 retains the same root angle (either 5 degrees 45 minutes for a No.2 or No.3 Phillips fastener, or 7 degrees for a No.1 Phillips fastener) and the same wing angle of 26 degrees 30 minutes according to standard Phillips specifications to ensure that the present bit 30 is fully compatible with standard Phillips-head fasteners. Thus, it will be appreciated that the present invention does not require a uniquely configured fastener to achieve its increased torque loading capabilities. Moreover, due to the radial symmetry of the present screwdriver bit 30, the increased torque loading capabilities of the present invention apply equally in both rotational directions of the driver.

[0021] Returning to the drawings, it will be noted from an examination of Figure 16 that the width of the radially outward facing surface 34 of the bit wing 32 remains substantially constant from the base 31 of the wing to the wing tip 35. This is contrary to the configuration of a standard Phillips bit, as illustrated in Figure 1, whose corresponding surface 14 gradually increases in width from the base 11 of the wing 12 to the wing tip 15 due to the geometry of the Phillips-standard root angle and the constant Phillips-standard included angle. Specifically, the improved Phillips-type bit 30 according to the present invention does not maintain a constant included angle from the base 31 of the wing 32 to the wing tip 35. Rather, as illustrated in Figure 17, the included angle between the bit wings 32 in the present screwdriver bit 30 is equal to the Phillips-standard 92 degrees at the base 31 of the bit wings 32 and progressively increases to approximately 105 degrees at the wing tips 35. In other words, rather than the side surfaces of the bit wings 12 being defined by flat planes as in the standard Phillips bit 10, the side surfaces of the bit wings 32 in the present bit 30 comprise generated surfaces. As a result, when the screwdriver bit 30 according to the present invention is inserted into the recess 20 of a standard Phillips-head fastener 24, a gradually increasing gap 38 (Figure 25) is defined between the bit wings 32 and the recess wings 21 in the radially outward directions. This is due to the fact that the thickness of the recess wings 21 in the standard Phillips-head fastener 24 diminishes more gradually in the radially outward direction due to the constant Phillips-standard included angle, which becomes progressively smaller than the increasing included angle of the present bit 30. In other words, the gap 38 shown in Figures 24 and 25 results from the fact that the included angle between the sidewalls of the recess wings 21 corresponds to the Phillips-standard 92 degrees whereas the included angle between the bit wings 32 at this illustrated axial position of bit 30 corresponds to approximately 103 degrees. (Note that the 103-degree angle referred to corresponds to the included angle at an axial position somewhat below the wing tip 35 as the entire bit portion typically does not fit into the recess 20 in the head of the fastener 24, as shown in Figure 27.) In addition, it is important to note that the radial dimension of the bit wings 32 when the bit is fully inserted into the recess 20 is less than that of the recess wings 21 so that a slight space is maintained between the radially outward facing surfaces 34 of the bit wings 32 and the opposing surfaces 4 of the recess wings 21. In the preferred embodiment of the present invention, the roots 36 of the recesses between adjoining bit wings 32 are also formed somewhat deeper to that an additional gap 40 (Figure 25) is created between the root 36 of the bit 30 and the root 42 of the recess 20 in the standard Phillips-head fastener 24. Finally, as illustrated in Figures 16 and 27, the base 31 of the present screwdriver bit 30 is preferably truncated as shown to prevent the bit 30 from bottoming out when inserted into the recess 20 of a standard Phillips-head fastener 24.

[0022] As a result of this configuration, when the present screwdriver bit 30 is inserted into the recess 20 of a standard Phillips-head fastener 24 and rotated in a clockwise direction, torque is applied to the fastener 24 along lines of contact 46 between the side surfaces of the bit wings 32 and the opposing side surfaces of the recess wings 20, as indicated by the arrows appearing in Figures 18-24. In addition, it will be appreciated that these initial lines of contact 46 between the side surfaces of the bit wings 32 and recess wings 20 are essentially parallel to the root 36 of the bit 30, as illustrated by the dashed lines in Figures 27. In other words, these lines of contact 46 form substantially the same 5-degree 45-minute angle with respect to the axis of the bit 30 corresponding to the Phillips-standard root angle. Moreover , as the level of applied torque increases and the bit 30 begins to deform the recess 20, the lines of contact expand radially outwardly in parallel fashion along the side faces of the bit wings 32, as indicated by the shaded portion 50 illustrated in Figure 29. This serves to significantly increase the level of torque that can be transmitted from the screwdriver bit 30 to the fastener 24 while confining the areas of engagement to the side surfaces of the bit wings 12. This distinction between the present invention and the standard Phillips bit is illustrated in Figures 14 and 26.

[0023] Significantly, the deformation of the recess 20, as illustrated in Figure 26, along the sidewalls of the recess wings 21 does not add to the relatively small cam-out forces generated by the application of torque along the initial lines of contact 46 between the bit 30 and recess 20. Accordingly, driving engagement between the screwdriver bit 30 and the fastener 24 can easily be maintained with the application of a modest amount of downforce. This phenomenon of the present invention is illustrated and diagrammed in Figures 27 and 28. As previously noted, the application of torque from the bit 30 to the fastener 24 along the initial lines of contact 46 on the side surfaces of the bit wings 32 is represented by the dotted lines in Figure 27. The application of force in this manner results in the generation of an outwardly directed force component perpendicular to the lines of contact, as indicated by the arrows 45 in Figure 27. This, in turn, results in the generation of an equal and opposite force vector designated "Z" in the accompanying vector force diagram shown in Figure 28. In view of the approximated 5-degree 45-minute angle of he force vector "Z" relative to the axis of the bit 30, the force vector "Z" is comprised predominantly of a horizontal force component, labelled "X", and a relative small vertical force component, labelled "Y". In fact, the vertical force component "Y" tending to cause the bit 30 to cam-out of the recess 20 is only equal to approximately a factor of 0.10 (i.e. sin 5 degrees 45') times the magnitude of the force vector "Z". Accordingly, when compared to a standard Phillips bit 10, significantly less downward force is required from the operator to retain the present bit 30 in the recess 20 of a standard Phillips-head fastener 24, even at high levels of applied torque.

[0024] From the above discussion, it will be appreciated that the screwdriver bit 30 according to the present invention is able to significantly reduce the cam-out force associated with a standard Phillips screwdriver bit 10 by preventing the radially outward facing bit wing surfaces 34 from contacting the recess 20 in the head 22 of the fastener 24. Due to the angle of these bit wing surfaces 324, the application of force along these surfaces is believed to be the greatest cause of cam-out in a standard Phillips design. Therefore, the present screwdriver bit 30 is capable of deforming the recess wings 21 in a Phillips -head fastener 24 to the degree illustrated in Figure 26 before significant cam-out forces will be generated. At these stage illustrated in Figure 26, torque is being applied along virtually the entire side surfaces of the bit wings 32 from the initial lines of contact 46 adjacent the root 36 of the bit to the outer radial edges 48 of the bit wings 32.

[0025] Finally, it will be appreciated that, in view of the radially symmetrical design of the invention, the present screwdriver bit 30 is capable of applying significantly greater torque loads than a standard Phillips bit in either rotational direction. Therefore, unlike certain existing modified Phillips designs which radially offset the bit wings and are, therefore, primarily usable in only one rotational direction, the present invention is equally useful for tightly setting standard Phillips screws and for "breaking free" and removing "frozen" Phillips fasteners.

[0026] While the above description constitutes the preferred embodiment of the invention , it will be appreciated that the invention is susceptible to modification, variation, and change without departing from the proper scope or fair meaning of the accompanying claims.

Claims

1. A driver for a standard Phillips-head fastener having a cross-shaped recess formed in the head thereof, the driver having associated therewith an axis and including a bit portion symmetrical about any plane containing the axis of the driver and adapted for insertion into said recess characterised in that it comprises
   radially symmetrical wing means having generated side surfaces and defining roots therebetween for rotationally driving said fastener on said side surfaces in the same manner in both rotational directions.

2. A driver according to Claim 1 wherein said wing means comprise four equally radially spaced bit wings defined by generated side surfaces that in turn define an included angle between adjoining bit wings that progressively increases from a first predetermine angle at the base of said bit wings to a second greater predetermined angle at an axially spaced distance therefrom.

3. A driver according to Claim 1 wherein the radially outwardly facing surfaces of said bit wings are tapered toward a common point at an angle relative to the axis of said bit portion substantially equal to the Philips-standard wing angle.

4. A driver according to Claim 1 wherein the roots of said bit portion are oriented relative to said bit axis at an angle substantially equal to the Phillips-standard root angle.

5. A driver according to Claim 4 wherein a gap is formed between said radially outward facing surfaces of said bit wings and the opposing outer radial surfaces of said recess when said bit portion is fully inserted into said recess.

6. A driver according to Claim 4 wherein a gap is formed between the root areas of said bit portion and the opposing surfaces of said recess when said bit portion is inserted into said recess.

7. A driver according to Claim 4 wherein the base of said bit portion is truncated.

8. A driver according to Claim 1 wherein said wing means are adapted to rotationally drive said fastener in both rotational directions initially adjacent said roots and progressively radially outward therefrom along said side surfaces as torque levels applied by said driver to said fastener increase.

9. A driver according to Claim 8 wherein said wing means initially engage said recess and drives said fastener along lines of contact adjacent and substantially parallel to said roots.

10. A driver according to Claim 1 for a standard Phillips-head fastener having a cross-shaped recess formed in the head thereof defining recess wings having outer radial surfaces that are tapered toward a common point at a predefined standard wing angle relative to the axis of the fastener the side surfaces of adjoining recess wings defining a predefined standard included angle that remains substantially constant from the bottom of said recess to the top of said recess and wherein the sidewalls of said recess wings are oriented at a predefined standard root angle relative to said axis such that the thickness of said recess wings expands in the axial direction from the bottom of the recess to the top of the recess; said driver including a bit portion adapted for insertion into said recess comprising:
   four bit wings having radially outward facing surfaces that are tapered toward a common point at an angle substantially equal to said standard wing angle relative to the axis of said bit portion and wherein the thickness of said bit wings adjacent the roots of said bit wings increases gradually in the axial direction at an angle approximately equal to said standard root angle but remains substantially constant along said tapered radially outward facing surfaces, and further wherein said generated side surfaces of said bit wings define an included angle in a plane substantially normal to said bit portion axis that progressively changes in the axial direction from a first angle adjacent the base of said bit wings to a second different angle adjacent the radially outer tips of said bit wings.

11. A driver according to Claim 10, wherein said bit wings define roots therebetween that are oriented relative to the axis of said bit at an angle substantially equal to said standard root angle.

12. A driver according to Claim 11, wherein said bit is adapted to engage said recess when said bit portion is inserted into said recess at the generated side surfaces of said bit wings along lines of contact adjacent and substantially parallel to said roots.

13. A driver according to Claim 12, wherein the area of engagement between the recess and said bit portion expands progressively radially outwardly from said lines of contact as the torque levels applied by said driver to said fastener increase.

14. A driver according to Claim 10, wherein a gap is formed between said radially outward facing surfaces of said bit wings and said opposing outer radial surfaces of said recess wings when said bit portion is fully inserted into said recess.

15. A driver according to Claim 10, wherein a gap is formed radially inward from said lines of contact between the roots of said bit portion and the opposing surfaces of said recess when said bit portion is fully inserted into said recess.

16. A driver according to Claim 10, wherein the base of said bit portion is truncated.

17. A driver according to Claim 10, wherein said bit wings are radially symmetrical such that equal levels of torque can be applied from said driver to the fastener in both rotational directions by all four bit wings.

Drawing