Patent Description:
Poor fit between the recessed socket area and the driver is also caused by anticorrosive coatings applied that may not be factored into design tolerance specifications. These coatings are often paints, applied by a "dip spin" method, which are thicker than zinc plating. The coatings shorten the depth the driver can extend into the recessed socket area which may cause premature cam-out due to a reduction in the surface contact that could be achieved absent a coating. Documents <CIT> and <CIT> disclose examples of fasteners and corresponding driving tools.

A fastener and a driver bit according to the invention are set out in claims <NUM> and <NUM>, respectively.

Methods and apparatus for a fastener head having a dual zone socket area and a mating driver bit according to aspects of the present technology include a fastener configured with driving surfaces adapted to provide enhanced engagement between each other during use. The fastener includes a recessed socket area with a sidewall that has an upper inwardly tapering section and a lower vertical section that extends to the bottom of the recessed socket area. The upper inwardly tapering section of the sidewall may also include an offset relative to the lower vertical section to create asymmetrical driving and removal surfaces. The technology also includes a corresponding mating driver bit configured with mating surfaces to the fastener to provide enhanced engagement between the fastener and mating driver bit. The technology also allows either the fastener or the driving bit to be used with preexisting fasteners and driver bits.

A more complete understanding of the present invention may be derived by referring to the detailed description when considered in connection with the following illustrative figures. In the following figures, like reference numbers refer to similar elements and steps throughout the figures.

The present technology may be described in terms of functional block components and various processing steps. Such functional blocks may be realized by any number of components configured to perform the specified functions and achieve the various results. For example, the present technology may employ various types of materials, fastening devices, driver systems and the like, which may carry out a variety of functions. In addition, the present technology may be practiced in conjunction with any number of processes such as the manufacture of fasteners, mechanical attachment, and torque transmitting systems, and the system described is merely one exemplary application for the invention. Further, the present technology may employ any number of conventional techniques for metalworking, component manufacturing, tooling fabrication, and/or forming surfaces.

Methods and apparatus for a fastener head having a dual zone socket area according to various aspects of the present technology may operate in conjunction with any suitable torque delivery system. Various representative implementations of the present technology may also be applied to any device capable of rotating fasteners, such as a driver bit, screwdriver, and the like.

Referring now to <FIG>, a fastener head <NUM> for a fastener such as a screw or bolt may comprise a recessed socket area <NUM> formed by a sidewall extending into the fastener head <NUM> and arranged around a longitudinal axis <NUM> of the fastener head <NUM>. The sidewall may comprise an upper edge <NUM> disposed along or proximate a top surface of the fastener head <NUM> and a lower edge <NUM> disposed at or proximate to a lower most section of the recessed socket area <NUM>. The sidewall may be configured in any suitable shape or dimension for receiving a driver bit <NUM> (see <FIG>) and may include one or more surfaces adapted to allow for the transfer of torque between the driver bit <NUM> and the fastener head <NUM>. The sidewall may comprise a plurality of torque surfaces upon which forces may be applied to turn the fastener head <NUM> in a clockwise (installation) direction or a counter-clockwise (removal) direction. For example, a driving surface <NUM> may comprise a first torque surface for receiving a driving force from the driver bit <NUM> when the fastener is being installed, or otherwise screwed into place, generally in a clockwise rotation. Similarly, a removal face <NUM> may comprise a second torque surface for receiving a removal force (e.g. counter-clockwise rotation) from the driver bit <NUM>.

The driving surface <NUM> provides a contact area for receiving an applied torque from the driver bit <NUM>. It is known that increasing a contact area along the driving surface <NUM> allows an applied torque to be more evenly distributed across the entire driving surface <NUM> and may allow for increased torque values while also making the recessed socket area <NUM> less susceptible to cam-out. The driving surface <NUM> may be configured to comprise any suitable shape or dimension. The driving surface <NUM> may comprise a substantially flat surface or the driving surface <NUM> may be formed by a curving surface. Similarly, the removal surface <NUM> provides a second contact area for receiving an applied torque from the driver bit <NUM>. The removal surface <NUM> may be configured to comprise any suitable shape or dimension.

The position and location of the driving and removal surfaces <NUM>, <NUM> are determined, at least in part, by the shape the sidewall makes around the longitudinal axis <NUM>. For example, referring now to <FIG> and <FIG>, for fasteners having a recessed socket area <NUM> with a sidewall arranged with straight wall segments <NUM> to form patterns such as triangles, squares, pentagons, hexagons, and the like, the driving and removal surfaces <NUM>, <NUM> are located on opposite sides of each wall segment <NUM>. Referring now to <FIG>, <FIG>, and <FIG>, for fasteners having a recessed socket area <NUM> with a sidewall arranged in a curvilinear line to form patterns having multi-lobular driving surfaces such as a <NUM> lobe Phillips, a <NUM> lobe Torx® design, or the like, the driving and removal surfaces <NUM>, <NUM> are located on opposite sides of each lobe <NUM>. One of ordinary skill in the art will recognize that these concepts can be applied to recessed socket areas <NUM> having any number of lobes <NUM> or straight walled segments <NUM>.

Referring now to <FIG>, the sidewall may also comprise an upper wall section <NUM> and a lower wall section <NUM>. The upper wall section <NUM> tapers inwardly from the upper edge <NUM> towards the longitudinal axis <NUM>. The taper of the upper wall section <NUM> creates a reduction in a cross-sectional area of the recessed socket area <NUM> between the upper edge <NUM> and a transition line <NUM> between the upper and lower wall sections <NUM>, <NUM>.

The upper wall section <NUM> may comprise a taper of between about <NUM>° (one degree) and about <NUM>° (three and three-fifths degrees) relative to the longitudinal axis <NUM>. For example, in one embodiment, the upper wall section <NUM> may taper inwardly by an angle of approximately <NUM>° (one and one-half degrees). In an alternative embodiment, the upper wall section <NUM> may taper inwardly by an angle of between <NUM>° (one and one-quarter degrees) and <NUM>° (one and one-half degrees).

The upper wall section <NUM> extends only partway down into the recessed socket area <NUM>. The depth that the upper wall section <NUM> extends into the recessed socket area <NUM> may be determined according to any suitable criteria such as a desired amount of contact area or a wedging affect between the fastener head <NUM> and an inserted driver bit. In one embodiment, the upper wall section <NUM> may comprise a height of less than half of the total depth of the recessed socket area <NUM>. For example, the upper wall section <NUM> comprises a height of about one-third the total depth of the recessed socket area <NUM>. In an alternative embodiment, the wall section <NUM> may comprise a height between one-quarter and three-quarters the total depth of the recessed socket area <NUM>.

The lower wall section <NUM> forms a vertical surface that extends from the transition line <NUM> to the lower edge <NUM>. The cross-sectional area of the recessed socket area <NUM> remains constant along the entire height of the lower wall section <NUM>. For example, referring now to <FIG>, in one embodiment the surfaces of the upper and lower wall sections <NUM>, <NUM> may be aligned with each other such that the cross-sectional area of the recessed socket area <NUM> is the same at any point along the height of the lower wall section <NUM>. This uniformity in cross-sectional area may allow for a prior art driver bit having completely vertical driving and removal surfaces to fit within the recessed socket area <NUM>.

Alternatively, and referring now to <FIG>, the cross-sectional area of the recessed socket area <NUM> along the lower wall section <NUM> may not remain constant along the entire height of the lower wall section <NUM> due to an offset between the lower wall section <NUM> and the upper wall section <NUM>. For example, the entire lower wall section <NUM> between the lower edge <NUM> and the transition line <NUM> may be rotated about the longitudinal axis <NUM> relative to the upper edge <NUM>. The resulting change to the surfaces of the upper and lower wall sections <NUM>, <NUM> creates a region of varying surface taper in the upper wall section <NUM> and a region of varying vertical height in the lower wall section <NUM>.

Referring now to <FIG>, in one embodiment, the lower edge <NUM> of a sidewall having six wall segments <NUM> may be rotated by between <NUM>° and <NUM>° (one degree and six degrees) in a generally clockwise direction about the longitudinal axis <NUM> relative to the upper edge <NUM>. Unlike the non-offset lower wall section <NUM> (see <FIG> and <FIG>) where each wall segment <NUM> has a uniform and generally rectangular surface area, the offset of the lower wall section <NUM> in this embodiment alters the surfaces of both the upper and lower wall sections <NUM>, <NUM> causing the transition line <NUM> to be angled downward contrary to the horizontal transition line <NUM> in the non-offset embodiment of <FIG>. The surfaces of the upper and lower wall section <NUM>, <NUM> take on more complex shapes causing an alteration in the size and shape of both the tapering region of the upper wall section <NUM> and the vertical region of the lower wall section <NUM>. With particular reference to the upper wall section <NUM>, the offset of the lower wall section <NUM> causes the surface of the tapering region to vary in height between the driving surface <NUM> and the removal surface <NUM>. Specifically, the a depth that the tapering region of the upper wall section <NUM> extends downward into the recessed socket area <NUM> is greater at the removal surface <NUM> than it is at the driving surface <NUM>. As a result, the upper wall section <NUM> extends more deeply into the recessed socket area <NUM> along the removal surface <NUM> portion of the sidewall than along the driving surface <NUM> portion of the sidewall.

Similarly, the vertical surface of the lower wall section <NUM> is altered such that a height of the vertical surface is greater along the driving surface <NUM> of the sidewall than it is along the removal surface <NUM>. Because upper wall section <NUM> comprises less taper at the driving surface <NUM>, a vertical, or substantially vertical, line of insertion <NUM> is formed between the upper edge <NUM> and the lower edge <NUM>. This near vertical line of insertion <NUM> may create a larger contact area along the entire driving surface <NUM> for the driving force to act on as compared the non-offset embodiment of <FIG>.

By maintaining the substantially vertical line of insertion <NUM> along the entire depth of the recessed socket area <NUM>, there is an increase in surface contact between the driver bit and the sidewall of the fastener head <NUM> when the driver bit is applying a force to tighten the fastener. The increased surface contact spreads the applied loads over a greater area and may prevent and/or reduce the likelihood that the driver bit will break during use or that the recessed socket area <NUM> may be prematurely worn as a result of point loading.

The extent to which the line of insertion <NUM> along the driving surface <NUM> of the lower wall section <NUM> is vertical along the entire depth of the recessed socket area <NUM> is determined based on the amount of offset or rotation between the lower wall section <NUM> and the upper wall section <NUM>. An offset that results in the lower edge <NUM> of the driving surface <NUM> of the lower wall section <NUM> aligning completely with the upper edge <NUM> will result in a completely vertical line of insertion <NUM>. For example, in one embodiment for a hex shaped recessed socket area <NUM>, the rotation of the lower wall section <NUM> relative to the upper wall section <NUM> to generate a completely vertical line of insertion <NUM> may be about <NUM>° (six degrees). Accordingly, an offset of less than <NUM>° (six degrees) results in a line of insertion <NUM> along the driving surface <NUM> that is not completely vertical but ends at some point below the upper edge <NUM> at the transition line <NUM> and is replaced by the tapering surface of the upper wall section <NUM>.

Referring now to <FIG>, the varying vertical and tapering regions for other embodiments formed by straight walled segments <NUM> is substantially the same as that described above for the embodiment having six equally sized straight walled segments <NUM>. The amount of offset required to obtain a completely vertical line of insertion <NUM> along the driving surface <NUM>, however, may vary according to the particular geometry of the wall segments <NUM>. For example, a fastener head <NUM> comprising a sidewall having three or four equally sized straight walled segments <NUM> may require a larger offset or rotation than a fastener head <NUM> having a sidewall comprising five or more equally sized straight walled segments <NUM>.

A natural result of creating a larger vertical line of insertion <NUM> along the driving surface <NUM> from the offset between the upper and lower wall sections <NUM>, <NUM> is that the amount of contact between an industry standard driver bit, such as a <NUM> hex key, and the recessed socket area <NUM> along the removal surface <NUM> is reduced. Referring again to <FIG>, in the non-offset embodiment, the vertical surface along both the driving and removal surfaces <NUM>, <NUM> is the same. This results in an identical amount of surface contact on the driving surface <NUM> during installation as on the removal surface <NUM> during removal of the fastener.

Conversely, and referring again to <FIG>, the offset creates a differing amount of surface contact between the driver bit and the driving and removal surfaces <NUM>, <NUM>. For example, if a hex key bit commonly known in the art is inserted into the recessed socket area <NUM> such that the driver bit extends into the lower wall section <NUM>, when a driving (clockwise rotation) force is applied the driver bit will contact the sidewall along the line of insertion <NUM>. In the case of the embodiments shown in <FIG>, the surface contact between the driver bit and the fastener head <NUM> along the line of insertion <NUM> may comprise the entire depth of the recessed socket area <NUM>. If a removal (counter-clockwise) force is applied, the driver bit will contact the sidewall of the recessed socket area <NUM> along the removal face <NUM> and due to the tapering region of the upper wall section <NUM>, the surface contact between the driver bit and the fastener head <NUM> will only exist in the portion of the lower wall section <NUM> that is below the transition line <NUM>. The implication of this configuration is that the removal force is spread over a smaller area than that of the driving force. Since it generally takes less removal force to loosen the fastener than is required to drive the fastener, the potential for breaking a prior art driver bit or causing premature wear/cam-out of the recessed socket area <NUM> is reduced.

With continued reference to <FIG>, if a driving bit having fully tapering walls (non-vertical) as commonly known in the art is inserted into the recessed socket area <NUM> then in addition to contact along the line of insertion <NUM>, the contact area between the recessed socket area <NUM> and the driving bit may be increased to include the tapering region of the upper wall section <NUM>. This increase in surface area contact would provide an increase along the removal face <NUM> allowing the driving and removal forces to be applied over a larger area.

Referring now to <FIG>, in an alternative embodiment having a curvilinear sidewall, the lower edge <NUM> of a sidewall having six lobes <NUM> is rotated by between <NUM>° and <NUM>° (one degree and six degrees) in a generally clockwise direction about the longitudinal axis <NUM> relative to the upper edge <NUM>. Unlike the non-offset lower wall section <NUM> (see <FIG> and <FIG>) where each lobe <NUM> comprises a uniform tapering section and vertical section, the offset of the lower wall section <NUM> in this embodiment alters the surfaces of both the upper and lower wall sections <NUM>, <NUM> resulting in a curvilinear transition line <NUM>. With particular reference to the upper wall section <NUM>, the offset of the lower wall section <NUM> causes the surface area of the taper to vary between the driving surface <NUM> and the removal surface <NUM> of each lobe <NUM>. Specifically, the surface area formed by the taper is greater on the removal surface <NUM> side of each lobe <NUM> than it is on the driving surface <NUM> side of the same lobe <NUM>. As described above, the tapered surface of the upper wall section <NUM> extends more deeply into the recessed socket area <NUM> along the removal surface <NUM> of each lobe <NUM> than along the driving surface <NUM> of each lobe <NUM>.

Similarly, the vertical surface of the lower wall section <NUM> is altered such that a height of the vertical surface is greater along the driving surface <NUM> of the sidewall than it is along the removal surface <NUM>. Because upper wall section <NUM> comprises less taper at the driving surface, a vertical, or substantially vertical, line of insertion <NUM> is formed between the upper edge <NUM> and the lower edge <NUM>. This near vertical line of insertion may <NUM> create a larger contact area along the entire driving surface <NUM> for the driving force to act on as compared the non-offset embodiment of <FIG> and <FIG>.

The extent to which the line of insertion <NUM> along the driving surface <NUM> of each lobe <NUM> is vertical along the entire depth of the recessed socket area <NUM> is determined based on the amount of offset or rotation between the lower wall section <NUM> and the upper wall section <NUM>. An offset that results in the lower edge <NUM> of the driving surface <NUM> of the lower wall section <NUM> aligning completely with the upper edge <NUM> will result in a completely vertical line of insertion <NUM>. For example, in one embodiment, the rotation of the lower wall section <NUM> relative to the upper wall section <NUM> to generate a completely vertical line of insertion <NUM> may be about <NUM>° (four degrees). Accordingly, an offset of less than <NUM>° (four degrees) results in a line of insertion <NUM> along the driving surface <NUM> that is not completely vertical but ends at some point below the upper edge <NUM> at the transition line <NUM> and is replaced by the tapering surface of the upper wall section <NUM>.

As described above for the straight walled segment embodiment, the offset creates a difference in the amount of surface contact between an inserted standard driver bit and the driving and removal surfaces <NUM>, <NUM>. The concept is the same in the curvilinear sidewall embodiment, except that the driving and removal surfaces <NUM>, <NUM> are disposed on opposing surfaces of each lobe <NUM> rather than along the same surface of the straight walled segment <NUM>. In addition, the tapering portion of the removal surface <NUM> tends to create a wedge fit directing a driving face of a typically tapered driver bit towards the line of insertion <NUM>.

Referring now to <FIG>, the driver bit <NUM> may comprise any suitable device or system for mating with the fastener head <NUM> to facilitate a transfer of torque from the driver bit <NUM> to the fastener head <NUM>. For example, the driver bit <NUM> may comprise a sidewall or curving multi-lobular surface configured to be selectively inserted into the recessed socket area <NUM> of the fastener head <NUM> and at least partially conform to the recessed socket area <NUM>. A fully conforming driver bit <NUM> comprising both a tapering section <NUM> and a vertical walled section <NUM> may create sufficient surface contact with the recessed socket area <NUM> to couple the driver bit <NUM> and the fastener head <NUM> together through a compressed, wedge, or "stick fit" such that the fastener head <NUM> does not fall off or otherwise automatically disengage from the driver bit <NUM> after the driver bit <NUM> has been inserted into the recessed socket area <NUM>. This design encourages the wedging effect towards the driving surface <NUM> along the tapering section <NUM>.

In an alternative embodiment, the driver bit <NUM> may comprise a longer tapering section <NUM> than that of the upper wall section <NUM> of the recessed socket area <NUM>. By including a longer tapering section <NUM>, the vertical walled section <NUM> of the driver bit <NUM> may be able to penetrate further into the lower wall section <NUM> of the recessed socket area <NUM> to provide greater surface contact across the lower wall section <NUM> despite the presence of any coatings on the driver bit <NUM> or the fastener head <NUM>. The tapering section <NUM> of the driver bit <NUM> may comprise the same degree of taper (between <NUM>° (one degree) and <NUM>° (three and one-half degrees)) towards a longitudinal axis <NUM> of the driver bit <NUM> as that of the upper wall section <NUM>.

In addition, the vertical walled section <NUM> may be sized such that it is slightly smaller than the size of a standard socket of a fastener head <NUM>. In one embodiment, the vertical walled section <NUM> of the driver bit <NUM> may be sized at about <NUM>%-<NUM>% of an intended corresponding socket area. For example, if the driver bit <NUM> is intended for use with a standard <NUM> hex socket, then the vertical walled section <NUM> may comprise an outermost radius of between <NUM> and <NUM>. The smaller size of the vertical walled section <NUM> accounts for the presence of any surface coatings that may be applied to the recessed socket area <NUM> of the fastener head <NUM> and/or on the surface of the driver bit <NUM> itself.

In yet another embodiment, the driver bit <NUM> may comprise only a tapering section <NUM>. For example, rather than include a vertical walled section <NUM> configured to match that of the lower wall section <NUM> of the fastener head <NUM>, the driver bit <NUM> may taper along the entire length of the sidewall or multi-lobular surface between a shank end and a bit end of the driver bit <NUM>. As described above, the end of the driver bit <NUM> may be sized at about <NUM>%-<NUM>% of an intended corresponding socket area to account for the presence of surface coatings.

Referring now to <FIG>, in yet another embodiment, the vertical walled section <NUM> may be offset from the tapering section <NUM>. The offset may be formed in a similar manner as described above with respect to the upper and lower wall sections <NUM>, <NUM> of the recessed socket area <NUM> except that the offset of the driver bit <NUM> may be in the opposite direction when viewed from the end of the driver bit <NUM>. This may create a substantially fully conforming surface engagement between the recessed socket area <NUM> and the sidewall of the driver bit <NUM>. More specifically, a surface height of the tapering section <NUM>, defined by a bit transition line <NUM> disposed between the tapering section <NUM> and the vertical wall section <NUM>, is greater at the removal surface <NUM> than the surface height is at the driving surface <NUM>. In other words, the tapering section <NUM> extends further towards the end of the driver bit <NUM> along the removal surface <NUM> portion driver bit <NUM> than along the driving surface <NUM>.

Further, the vertical surface of the vertical walled section <NUM> is altered such that a height of the vertical surface is greater along the driving surface <NUM> of the sidewall than it is along the removal surface <NUM>. Because the tapering section <NUM> comprises less surface area along the driving surface <NUM>, a vertical, or substantially vertical, line of insertion may be formed between a shank end of the driver bit <NUM> and an end of the vertical walled section <NUM> of the driver bit <NUM>. This near vertical line of insertion may create a larger contact area along the entire driving surface <NUM> for the driving force to act on as compared the non-offset embodiment of <FIG>.

When embodiments of the driver bit <NUM> shown in <FIG> are used in conjunction with mating fastener heads <NUM> represented by <FIG>, the surface areas formed by the tapering and vertical portions act to enhance a "stick-fit" feature of the components. For example, referring now to <FIG>, <FIG>, the tapering sections <NUM> and the vertical wall sections <NUM> of the driver bit <NUM> each form triangular shaped surface areas. Similarly, the upper and lower wall sections <NUM>, <NUM> of the recessed socket area <NUM> also form triangular surface areas. The triangular surface areas may largely conform to each other to create triangular intersections areas when the driver bit <NUM> is inserted into the recessed socket area <NUM>. The triangular intersections areas provide much greater surface contact between the driver bit <NUM> and the fastener head <NUM> than can be achieved through other commonly used methods of creating a wedge or "stick-fit" that only fall along a vertical or horizontal line of contact. The larger contact area allows the driver bit <NUM> to hold the fastener straighter and with better grip than existing wedge or "stick-fit" designs. Better grip between the driver bit <NUM> and the fastener head <NUM> provides increased benefits for machines such as robotic usage since the faster is held more tightly and straighter after the driver bit <NUM> is inserted into the recessed socket area <NUM>.

Referring now to <FIG>, in an embodiment where the sidewall of the driver bit <NUM> comprises a curvilinear sidewall forming a multi-lobular surface and the vertical walled section <NUM> is offset from the tapering section <NUM>, the surfaces of both the tapering and vertical walled sections <NUM>, <NUM> form a curvilinear bit transition line <NUM>. This causes the height of the tapered surface to differ between the driving surface <NUM> and the removal surface <NUM> of each lobe <NUM>. As with the previous embodiment, the surface height formed by the taper is greater on the removal surface <NUM> of each lobe <NUM> than it is on the driving surface <NUM> of each lobe <NUM>. As described above, the tapered surface of the tapering section <NUM> extends further down the length of the multi-lobular surface of the driver bit <NUM> along the removal surface <NUM> of each lobe <NUM> than along the driving surface <NUM> of each lobe <NUM>.

Similarly, the vertical surface of the vertical walled section <NUM> is altered such that the height of the vertical surface is greater along the driving surface <NUM> of each lobe <NUM> than it is along the removal surface <NUM> of the lobe <NUM>. Because the tapering section <NUM> comprises less taper along the driving surface <NUM>, a vertical, or substantially vertical, line of insertion may be formed between the shank end and the end of the driver bit <NUM>. This near vertical line of insertion may create a larger contact area along the entire driving surface <NUM> for the driving force to act on as compared the non-offset embodiment of <FIG>.

The particular implementations shown and described are illustrative of the invention and its best mode and are not intended to otherwise limit the scope of the present technology in any way. Indeed, for the sake of brevity, conventional manufacturing, connection, preparation, and other functional aspects of the system may not be described in detail. Furthermore, the connecting lines shown in the various figures are intended to represent exemplary functional relationships and/or steps between the various elements. Many alternative or additional functional relationships or physical connections may be present in a practical system.

In the foregoing specification, the technology has been described with reference to specific exemplary embodiments. Various modifications and changes may be made, however, without departing from the scope of the present technology as set forth in the claims. The specification and figures are illustrative, rather than restrictive, and modifications are intended to be included within the scope of the present invention. Accordingly, the scope of the technology should be determined by the claims rather than by merely the examples described.

For example, the steps recited in any method or process claims may be executed in any order and are not limited to the specific order presented in the claims unless specifically recited in the claims. Additionally, the components and/or elements recited in any apparatus claims may be assembled or otherwise operationally configured in a variety of permutations and are accordingly not limited to the specific configuration recited in the claims. Benefits, other advantages and solutions to problems have been described above with regard to particular embodiments; however, any benefit, advantage, solution to problem or any element that may cause any particular benefit, advantage or solution to occur or to become more pronounced are not to be construed as critical, required or essential features or components of any or all the claims.

Claim 1:
A fastener having a head portion (<NUM>) with a recessed socket area (<NUM>) extending into the head portion (<NUM>) and a shank sharing a longitudinal axis (<NUM>) with the recessed socket area (<NUM>), comprising:
a sidewall defining the recessed socket area (<NUM>) having a top edge (<NUM>) and a bottom edge (<NUM>); and
a plurality of driving surfaces and removal surfaces disposed along the sidewall, wherein:
an upper section (<NUM>) of the sidewall tapers inwardly towards the longitudinal axis (<NUM>) between about one degree and about three and three-fifths degrees from the top edge (<NUM>) to a curvilinear transition line (<NUM>); and
a lower section (<NUM>) of the sidewall forms a vertical surface relative to the longitudinal axis (<NUM>) and is disposed between the curvilinear transition line (<NUM>) and the bottom edge (<NUM>), wherein:
the lower section (<NUM>) of the sidewall is offset in the clockwise direction from the upper section (<NUM>) of the sidewall by a rotation of between one degree and six degrees causing the curvilinear transition line (<NUM>) to vary along a length of the plurality of driving surfaces and removal surfaces between the top edge (<NUM>) and the bottom edge (<NUM>); and
a driving surface of the lower section (<NUM>) of the sidewall at the bottom edge is aligned with a driving surface of the upper section (<NUM>) of the sidewall to form a vertical line of insertion extending from the top edge (<NUM>) to the bottom edge (<NUM>).