GB2360234A - Improved screw driver bit - Google Patents

Abstract

An improved screw driver bit comprises a shank 2 and a blade 3 connected by an articulated constant velocity joint allowing substantially constant velocity transmission of rotary forces and transmission of pressure between the shank 2 and blade 3 and allowing relative angular movement between the shank and blade perpendicular to the axis of rotation through a predetermined range so that when an engagement element on the blade is brought into contact with the head 5a of a threaded fastener the articulated joint allows the blade to automatically orient itself for correct engagement with the threaded fastener 5.

Description

2360234 Improved Screw Driver Bit This invention relates to an improved

screw driver bit, and in particular to an improved screw driver bit for use with powered screw drivers.

A common problem in driving screws is the screw driver bit slipping out of engagement with the screw head, normally resulting in damage to the screw head and/or bit. When the bit becomes completely disengaged from the screw head the bit can slip right off the screw head, which can result in further damage to the surface the screw is being driven into or through as the bit slides across or impacts the surface.

This problem is commonly encountered in manually driving screws but it is a more significant problem where power tools are used to drive screws because of the poor feedback to the operator from the contact between the screw driver bit and the screw head and the longer reaction time required to stop.

Where a screw driver and screw head are in good condition the tendency of the screw driver bit to slip away from and become disengaged from the screw head is generally a consequence of misalignment between the screw head and the bit. This is a particular problem for slotted screws.

Other forms of screw driver bit, when used with matching screw head engagement structure, are normally more tolerant of misalignment or are physically harder to misalign because they give a more positive location of the drill bit to the screw head, but there is still a tendency for a misaligned screw driver bit to work its way out of the screw head as the screw is driven.

This invention is intended to provide a screw driver bit overcoming these problems, at least in part.

2 This invention provides a driver bit for driving threaded fasteners comprising a shank and a blade connected by an articulated joint allowing rotary forces about a tirst axis and pressure parallel to said axis to be transmitted between the shank and blade and allowing relative angular movement between the shank and blade through a predetermined range about the two axes perpendicular to said first axis, the blade having an engagement element arranged to engage with a threaded fastener and the articulated joint being a substantially constant velocity joint for rotary movement about said first axis for relative movement within said predetermined range.

This arrangement provides a driver bit for threaded fasteners having a blade able to automatically conform to the orientation of the fastener and so compensate for misalignment of the driver bit in the fastener ensuring good and reliable engagement.

Embodiments of the invention will now be described by way of example only with reference to the accompanying diagrammatic figures in which:

Figure 1 shows a partially cut-away side view of a screw driver bit according to a first embodiment of the invention; Figure 2 shows a side view of the shank of the bit of Figure 1; Figure 3a shows a side view of a blade of the bit of Figure 1; Figure 3b shows a further side view of the blade of Figure 3a from a direction perpendicular to the view of Figure 3a; Figure 3c shows a top view of the blade of Figure 3a; Figure 3d shows a cross-section along the line AA in Figure 3c; Figure 4 is a partially cut-away side view of the bit of Figure 1 in use; 3 Figure 5 shows a partially cut-away side view of a bit according to a second embodiment of the invention; Figure 6 shows a partially cut-away side view of a screw driver bit according to a third embodiment of the invention; Figure 7 shows a cross-sectional view of an alternative blade suitable for use in the screw driver bits of the first three embodiments; Figure 8 shows a side view of an alternative screw driver blade tip suitable for use in the invention; Figure 9 shows a side view of the tip of Figure 8 from a direction perpendicular to the view of Figure 8; and Figure 10 shows a side view of the blade tip of Figure 8 in use.

A first embodiment of a screw driver bit according to the invention is shown in Figures 1 to 4.

The inventive screw driver bit is an articulated screw driver bit 1 having an articulating joint close to the bit end where the screw driver bit 1 is intended to engage a screw head. The articulated screw driver bit 1 is shown with the blade 3 partially cut away in Figure 1. The shank 2 is shown in Figure 2. Side views of the bit 3 from two perpendicular directions are shown in Figures 3a and 3b. Figure 3c shows a top view of the blade 3 and Figure 3d shows a cross-sectional view of the blade 3.

The cross section of Figure 3d is taken perpendicularly to the cut-away view of Figure 1.

The shank 2 has an upper section 2a formed as a standard "E" type shank having a hexagonal cross-section and a diameter between opposed flat faces of 0.25in (approx 4 6.35mm). The upper hexagonal section 2a is intended to be inserted into a chuck or hexagonal driving socket to allow the screw driver bit 1 to be driven. The upper hexagonal section 2a has a recessed band 2b part way along its length to allow easy insertion and removal into a hexagonal drive socket, as is conventional in detachable screw driver bits.

The shank 2 further comprises a circular cross-section shaft 2c having a smaller diameter than the hexagonal section 2e and extending from the upper hexagonal section 2a. The shaft 2c ends at its lower end remote from the upper hexagonal section 2a in a ball end 2d.

The ball end 2d is a generally spherical shape having a spherical end surf&ce 2e at its lower end. Moving along the shank 2 away from the lower end the spherical end surface 2e is blended into a hexagonal crosssection band at the broadest part of the spherical end surface 2e, as measured moving along the axis of the shank 2. The ball section 2d then narrows in further to a neck portion 2g before broadening back out into the circular shaft 2c.

The shape of the ball section 2d in this example can be best visualised as a substantially spherical shape with a band of flat surfaces arranged in a hexagon forming a narrow band around a circumference of the sphere so that the band lies in a plane perpendicular to the axis of the shank 2.

The blade 3 comprises a cylindrical body section 3a ending in a conventional screw driver flat blade tip 3b suitable to engage a conventional slot head screw.

The cylindrical body section 3a of the blade 3 contains a series of recesses intended to receive a shank 2. The recesses in the blade section 3 comprise a first large recess 3c so that the upper section of the blade body 3a is a thin-walled cylindrical tube. On the end of the recess 3c is a flirther recess comprising a first hexagonal section 3d formed as a hexagonal recess coaxial with the cylindrical recess 3c and ending in a second concave hemispherical section 3e below the first hexagonal section 3d.

The concave hemispherical section 3e is sized to match the spherical end section 2.e of the ball end 2d while the hexagonal recess section 3d is arranged to engage with the hexagonal band 2f of the ball end 2d.

The internal diameter of the cylindrical recess section 3c of the blade 3 is larger than the external diameter of the shaft 2c of the shank 2 to leave a clearance between them to allow for relative angular movement of the shank 2 and blade 3. A resilient 0 ring 4 is held in this cylindrical gap between the shank 2 and the blade 3.

The resilient 0 ring 4 can be formed of rubber or a rubber like synthetic material such as neoprene or urethane.

In use, the articulated screw driver bit 1 is inserted into a conventional hexagonal bit receiving socket on a manual or electric screw driver or held in the chuck of an electric drill with a suitable speed control. The hexagonal end section 2a of the shank 2 engages with the hexagonal bit receiving socket or chuck.

The articulated screw driver bit 1 is then moved into contact with a head of a screw 5 so that the blade tip 3b passes into the slot 5a of the screw head and bears against the base of the slot 5a.

If the axis of the screw driver bit 1 is not parallel to the axis of the screw 5, as the screw driver bit 1 is urged into contact with the screw 5 the pressure transmitted along the shank 2 through the spherical end surface 2e of the ball end 2d and the opposed 6 concave spherical recess section 3e of the blade 3 will cause the blade 3 to rotate relative to the shank 2 until the blade tip 3b is correctly orientated relative to the screw 5 so that the end of the blade 3b lies in continuous contact with the bottom of the slot 5a in the head of the screw 5, as shown in Figure 4.

This rotation of the screw driver blade 3 relative to the shank 2 is allowed for by the clearance between the inside of the recess 3c and the circular section of the shank 2. The 0 ring 4 compresses as required to accommodate the relative rotational movement of the blade 3 and shank 2.

When it is attempted to drive the screw 5 through the screw driver bit 1 the necessary pressure to keep the tip 3b of the blade 3 engaged in the slot of the screw 5, and when driving a self tapping screw into a surface, the necessary pressure to help keep the screw engaged, is transmitted along the shank 2, through the spherical end surface 2e of the ball 2d and the cooperating hemispherical recess section 3e and then through the blade tip 3b to the base of the slot and into the screw. The rotary force to drive the screw is transmitted along the shank 2 and then by engagement of the hexagon of flat surfaces of the hexagonal band 2f of the ball 2d with the cooperating hexagon of flat surfaces of the hexagonal section 3d. into the blade 3 and then through the sides of the blade tip 3b to the sides of the slot in the head of the screw 5.

Where the angle between the axis of rotation of the screw 5 and the axis of the shank 2 of the screw driver bit 1 is relatively small the engagement of the two sets of hexagonal faces 2f and 3d acts as an effectively constant velocity joint transmitting rotational movement of the shank 2 to the blade 3.

7 In order to optimise the self aligning action of the articulated screw driver bit 1 the pressure contact point between the shank 2 and the blade 3, in the illustrated embodiment the contact point between the spherical end 2e of the ball 2d of the shank 2 and the hemispherical recess section 3e in the blade 3, should be as close to the blade tip 3b as possible. The pressure contact point should be only a few millimetres from the end of the blade tip. Preferably less than 1Omm and more preferably less than 5mm.

The amount of misalignment which can be compensated for by the articulated screw driver bit 1 is limited to the amount by which the axis of the shank 2 and bit 3 are able to diverge and this is in turn limited by the geometry of the shank 2 and bit 3. In the illustrated embodiment the maximum angle between the shank 2 and the blade 3 is set by the clearance between the inner wall of the recess 3c of the blade 3 and the shaft 2c of the shank 2 which will come into mutual contact when the maximum limiting angle is reached.

It is preferred to limit the amount of angular movement available between the shank 2 and blade 3 to 10' or less, giving a maximum range of relative angular movement in any plane of 201 or less. This ensures that the joint between the shank 2 and blade 3 is able to act as an effectively constant velocity joint.

The 0 ring 4 is held in position between the shank 2 and the blade 3 by being glued around its inner and outer circumferences to the inner surface of the blade 3 and the outer surface of the shank 2 respectively. Such gluing could be replaced by other securing methods such as contact welding or the keying of parts of the 0 ring into recesses in the respective surfaces if necessary.

8 It will be appreciated that in the described embodiment the blade 3 is prevented ftom being pulled off the shank 2 only by the 0 ring 4. In order to provide a more robust attachment of the blade 3 to the shank 2 other retaining means such as clips or circlips could be used.

The recess 3c contains a grease or other lubricant to minimise wear at the contact surfaces between the shank 2 and blade 3 and this grease or other lubricant is retained by the 0 ring 4. The 0 ring 4 also prevents grit and other foreign objects penetrating the recess 3 c between the shank 2 and blade 3, which could jam the articulated screw driver bit and prevent its self aligning action. Finally, the 0 ring 4 provides a resilient urging of the blade 3 which will tend to return the blade 3 to a position co-axial with the shank 2. This self-centering action makes the self-aligning screw driver bit 1 easier to use by simplifying lining up the bit with a screw.

In this embodiment the blade 3 comprises a tip 3b formed as a conventional blade with a rectangular end cross-section so that the articulated bit 1 can be used to drive screws with a slot head.

This tip 3b, of the blade 3 could be replaced by alternative screw driving tips. Examples of suitable screw driving tips which can be employed include posidrive, supadrive, torx, Philips cross-head and hexagonal Allen key type screw driver tips. It should be noted that this list is exemplary and not exhaustive.

A second embodiment of a screw driver bit according to the invention is shown in Figure 5.

The articulated screw driver bit 11 of the second embodiment comprises a shank 2 identical to the shank of the first embodiment together with a blade 13.

9 The blade 13 comprises a cylindrical body section 13a ending in a conventional screw driver flat blade tip 13b suitable for engaging a conventional slot head screw.

The cylindrical body section 13a of the blade 13 contains a recess intended to receive the shank 2. The recess in the blade section 13 is a substantially part spherical recess 13f comprising a base section formed as a concave hemispherical recess section 13e, a middle section formed as a hexagonal section 13d coaxial with the hemispherical section 13e and an upper section 13g extending upwards and inwards from the hexagonal section to define a circular aperture 13h having a narrower diameter than the hemispherical section 13e and the ball end 2d of the shank 2.

The upper section 13g has an internal surface defining part of the surface of the cavity 13f and is a partially spherical surface having a larger diameter than the concave hemispherical section 13e.

The inwardly projecting section 13g is formed by swaging to form an enclosure retaining the blade 13 attached to the shank 2.

The available range of movement of the blade 13 relative to the shank 2 will be limited by contact of the edge of the circular aperture 13h defined by the inwardly projecting section 13g contacting the neck portion 2g of the shank 2.

The inwardly projecting section 13g of the blade 3 can be a series of separate inwardly projecting fingers or- a continuous circular section.

Operation of the articulated screw driver bit 11 is the same as use of the articulated screw driver bit 1 according to the first embodiment.

A resilient means such as an 0 ring or resilient shroud will be attached between the shank 2 and blade 13, but such resilient means are not shown in Figure 5 for clarity.

This resilient means would carry out the same functions of the 0 ring 4 in the first embodiment of retaining lubricant, preventing entry of foreign objects and providing a resilient self centering action tending to return the blade 13 to a position coaxial with the shank 2. However, the blade 13 will be retained on the shank 2 by the projecting section 13g so that the resilient means is not the primary means retaining the blade 13 on the shank 2.

Under certain circumstances the articulation of the blade relative to the shank in the articulated screw driver bits of the first and second embodiments could be a disadvantage. One such situation would be when self tapping wood or chipboard screws are being started to be driven into a surface. In this situation it is useful to be able to rigidly lock the shank and blade together against relative pivoting movement in order to allow the screw to be directionally stabilised by the screw driver bit until the screw is properly started and supported by the material it is being screwed into.

A third embodiment in the invention providing a screw driver bit having such a locking function is shown in Figure 6.

The lockable articulated screw driver bit 21 is based on the articulated screw driver bit of the first embodiment shown in Figures 1 to 4.

The lockable articulated screw driver blade 21 comprises a shank 2 and a blade 23. The blade 23 is substanti-ally the same as the blade 3 of the first embodiment except that the 0 ring 4 is located deeper inside the recess 23c within the blade 23 to leave an annular cavity 24 above the 0 ring 4.

A sliding collar 25 is mounted on the circular shaft 2c of the shank 2 and is arranged to be slidingly movable between a first non-locking position shown in Figure 6 11 in which the collar 25 is clear of the blade 23 and second locking position in which the lower end of the collar 25 is located within the annular cavity 24 so that the blade 23 is held coaxial with the shank 2.

The sliding collar 25 is urged into the first position in which it does not interfere with relative movement of the shank 2 and blade 23 by a spring 28 held in compreGsion between the sliding collar 25 and a circlip 26 on the shaft 2c of the shank 2.

In use, if the user wishes to hold the blade 23 rigidly coaxial relative to the shank 2, for example when starting a wood screw, the collar 25 is manually pushed forward into the second locking position to engage and lock the blade 23. Then, when locking is no longer required the user releases the collar 25 and the spring 27 will automatically urge the collar 25 back to the first position where pivoting movement of the blade 23 relative to the shank 2 to correct for misalignment can take place.

The circlip 26 could be replaced by a flange formed on the shaft 2, but the use of a circlip is preferred because this simplifies assembly.

In order to prevent foreign objects entering the annular cavity 24 and jamming the articulated screw driver bit 2 1, the screw driver bit 21 should be arranged so that the clearance between the sliding collar 25 and the blade 23 is as small as possible when the sliding collar 25 is in the first position.

A suitable material for the sliding collar 25 is hard nylon.

It will be appreciated by the person skilled in the art that alternative lockilLg arrangements such as a sliding collar fitting over the outside of the blade would be possible. Similarly, it will be realised that similar locking arrangements could be added to the screw driver bit 11 according to the second embodiment of the invention.

12 As discussed above, in order to stabilise the blade it is desirable to have the pressure contact point between the shank and the blade as close to the blade tip as possible.

An alternative arrangement of the blade which allows the pressure contact point to be brought closer to the blade tip 3b, is shown in Figure 7. This alternative blade structure can be substituted for the blade in any of the previous embodiments.

The alternative blade 33 includes a hexagonal recess 33d similar to the previous embodiments. However, instead of the concave hemispherical surface of the previous embodiments a small diameter cylindrical socket 34 is formed. The socket 34 contains a ball bearing 35. The diameter of the cylindrical socket 34 is arranged to be just sufficient to allow the ball bearing 35 to be fitted into the socket 34. The depth of the socket 34 is set relative to the diameter of the ball bearing 35 so that when the shank 2 is located within the blade 33 the end surface 2e of the shank 2 bears on the ball bearing 35 so that pressure forces transmitted along the shank 2 are transmitted to the blade 33 only through the ball bearing 35.

In this embodiment the pressure contact point is effectively the contact point between the ball bearing 35 and the base of the recess 34. This is closer to the blade tip than can be achieved in the previous embodiments, improving the efficiency of the self aligning action.

Although the self aligning articulated screw driver bits as described above are highly effective it has been found that they are more effective for screw head types which stabilise the screw driver relative to the head in orthogonal directions such as Philips cross-head, posidrive, Allen key etc, than for the conventional slot headed screw. This is 13 believed to be because a conventional slot head screw only stabilises the connection between the screw and the screw driver in one direction.

As a result, under some circumstances the self alignment of the articulated screw driver bits described above may be less effective when the screw driver is driving a s lot head screw.

It is believed that this is because when the articulated screw driver bit is being used to drive a slot head screw with a conventional rectangular cross-section ended tip which passes into and bears on the bottom of the slot, the forces generated by contact between the tip and the slot base will tend to generate a relatively large force operative to move the articulated screw driver bit and hold it in alignment with the screw head if the misalignment is oriented such that it would tend to pivot the tip away from the slot base in a plane parallel to the long axis of the tip. On the other hand only relatively small forces are generated when the orientation of the misalignment is orthogonal to this, that is in the plane of the short axis of the tip cross-section.

In order to avoid this problem and ensure that the articulated screw driver bit is held in good engagement with a slotted screw head for all orientations of misalignment an alternative blade tip 40 as shown in Figures 8, 9 and 10 can be employed for slot headed screws.

The blade tip 40 comprises a conventional rectangular cross-section ended blade section 41 cooperates with a slot 5a of a screw 5.

The improved blade tip 40 also comprises a pair of stabilising ribs 42 extending from the sides of the blade 41 perpendicularly to the blade 41. The ribs 42 do not extend as far forwards as the blade 41 so that when the blade 41 passes into the slot 5a on the 14 screw 5 and is in contact with the base of the slot 5a the ribs 42 are slightly spaced from the surface 5b of the screw head.

If the blade tip 40 is misaligned relative to the screw 5 in a plane perpendicular to the slot 5a one of the ribs 42 will contact the end face 5b of the screw head to generate an aligning force tending to urge the articulated screw driver bit into proper engagement with the screw 5.

Use of the articulated self aligning screw driver bits according to the invention allows perfect alignment of the contacting parts of the screw driver bit and a screw head even when there is misaligriment or sideways movement of the screw driver relative to the screw. This ensures that there is always the maximum possible grip provided between the screw driver bit and the screw, reducing the risk of separation of the screw driver bit from the screw and consequent damage to the screw driver bit, screw or surrounding surfaces.

In a conventional rigid screw driver bit the bit has to simultaneously perform three functions. Firstly, grip between the bit and fastener must be provided, secondly pressure must be carried from the operator to the fastener and thirdly the fastener must be turned in the required direction.

The grip between the bit and the screw is highly dependent on the alignment between the two and any deviation from a geometrically perfect arrangement relative to the screw will usually result in slippage of the bit from the screw and possibly cause damage to bit, screw or surrounding surfaces.

This arrangement is complicated to achieve in practice by the fact that the perfect geometrical position of the bit relative to the fastener may vary during driving or removing of the screw, for example if the screw is entering a surface at a slight angle.

The use of articulated screw driver bits according to the invention provides the advantages that these functions are separated. Once the bit has been engaged to the screw the alignment between the screw and the bit is automatically arranged to be correct, or as close to correct as is possible for the allowed range or articulation of the bit. Pressure from the operator carried to the fastener is concentrated at the pressure contact point just above the point of contact with the screw for subsequent dissipation into the screw. The turning of the screw by the bit is carried as before.

Unlike a conventional bit, with the inventive articulated bit the more pressure that is applied the more effective the self-alignment becomes. lt should be noted that the instinctive reaction of most people to slippage is to increase the pressure. In the case of a conventional rigid bit this instinctive reaction may result in slippage becoming worse, but using articulated bits according to the present invention this instinctive reaction will normally assist in preventing slippage. Movement of the bit shank away from a geometrically perfect relationship with the screw caused by operator error or movement of the screw no longer affects the engagement between the working end or blade of the articulated bit and the screw. -Moreover, whatever grip is obtainable between the bit and the screw can be utilised fully at all times and throughout the rotation of the screw driver. This simplifies the screw tightening or releasing operation because all the user has to do is to provide as much pressure as required and rotate the screw driver without considering the precise alignment of the screw driver to the screw. Of course, as explained above 16 there is a limit to the amount of misalignment that can be absorbed by the articulated selfaligning bit so that there will still be problems if there is a very large degree of misalignment.

The use of a conventional E type shank is convenient because this will fit conventional powered and manual screw driver sockets but the use of other sizes or types of shank is possible. Further, the use of a shank comprisin. a hexagonal drive section together with a circular shaft, a neck section and a ball end is convenient but not essential. In particular the neck section could be omitted. Other arrangements would also be possible.

The description discloses embodiments of the invention providing screw driver bits. The invention is also applicable to drivers intended for any form of threaded fastener in which the driver engages with an end of the fastener.

In the described embodiments the bits are detachable bits intended to be releasably attached in a hexagonal socket of a manual or powered screw driver or a drill chuck. The invention would of course be equally applicable to a screw driver bit integrally formed into a screw driver and such an integral manual screw driver could be provided simply by ending the shank in the described embodiments in a handle rather than hexagonal engagement section.

In the described embodiments a substantially constant velocity drive, at least for low angles of rotation between the shank and blade is provided by the engagement of hexagonal flat faces on the shank and blade. It will be appreciated by the person skilled in the art that other constant velocity rotary drive arrangements are possible. One 17 possible such arrangement would be the use of cooperating splines on the shank and blade.

It should be noted that the different technical features of the various embodiments described could be combined and exchanged.

It will be appreciated by the person skilled in the art that there are many alternative mechanical arrangements which could be used to provide the invention and that the described embodiments are examples only.

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Claims (17)

Claims:

1. A driver bit for driving threaded fasteners comprising a shank and a blade connected by an articulated joint allowing rotary forces about a first axis and pressure parallel to said axis to be transmitted between the shank and blade and allowing relative angular movement between the shank and blade through a predetermined range about the two axes perpendicular to said first axis, the blade having an engagement element arranged to engage with a threaded fastener and the articulated joint being a substantially constant velocity joint for rotary movement about said first axis for relative movement within said predetermined range.

2. A driver bit as claimed in claim 1, in which the shank includes an engagement section for engaging a driving mechanism.

3. A driver bit as claimed in claim 1 or claim 2, in which said first axis is a longitudinal axis of the shank and the engagement element of the blade is arranged to engage with a threaded fastener and drive it about a second axis.

4. A driver bit as claimed in claim 3, in which the predetermined range of relative angular movement allows the first and second axes to diverge by a maximum of IT.

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5. A driver bit as claimed in claim 3 or claim 4, and further comprising a resilient means acting between the blade and shank to urge the blade and shank towards a position where the first and second axes are coaxial.

6. A driver bit as claimed in any one of claims 3 to 5, and further comprising releasable locking means able to releasably lock the blade and shank in a position where the first and second axes are coaxial.

7. A driver bit as claimed in any preceding claim, in which pressure along the first axis between the shank and blade is transmitted through a sliding contact point between mutually opposed surfaces of the shank and blade.

8. A driver bit as claimed in any preceding claim, in which the sliding contact point is less then 1 cm from the tip of the engagement element.

9. A driver bit as claimed in claim 8, in which the sliding contact point is less than 5mm from the tip of the engagement element.

10. A driver bit as clainfed in any preceding claim in which the engagement element comprises a rectangular cross-section tip suitable for engagement with a slot and ribs extending from and shorter than the tip extending perpendicularly to the long axis of the tip.

11. A driver bit as claimed in any preceding claim in which the driver bit is a screw driver bit.

12. A screw driver incorporating a screw driver bit as claimed in claim 11.

13. A driver bit substantially as shown in or as described with reference to Figures 1 to 4.

14. A driver bit substantially as shown in or as described with reference to Figure 5.

15. A driver bit substantially as shown in or as described with reference to Figure 6.

16. A driver bit substantially as shown in or as described with reference to Figure 7.

17. A driver bit substantially as shown in or as described with reference to Figures 8 to 10.