The present invention relates tc im rever fastener, and relates in particular, thcugn not exclusively, to a threaded fastener suitable fcr fastening a grinding wnee_ , circular saw blade or carving disc tc the spindle cf a rcwer tool.

BACKGROUND TO THE irrEL ICπ

With a conventional threaded fastener, fcr example, in the form cf a nut, a significant proportion cf tne energy required to tighten the nut on a threaded spindle cf a :lr or the like, is dissipated due to friction between the nut and the surface of an object tc be fastened. This means tr.e the torque required to achieve the necessary "tightness ^' „: t. ; nut, (ie. the hold-down pressure exerted by the ri c:. tr.e ob ect to be fastened) , can be up to fifty percent greater tnan would otherwise be necessary. For th s reason, -special tools such as, for example, a long spanner or an adjustable tcr ue- wrench, are used to provide the torque necessary tc cverc._.τe the friction and still achieve the desired hold-down preεεuze. For the same reason a special tool is usually required tc unfasten the nut as well.

It was hitherto thought that maximum friction is required between the nut and the fastened object m order tc ensure that the nut and/or the object did not come unfastened in use. A recent discovery suggests that this may not oe the case, and that provided sufficient hclά-άowr, pressure is exerted by the action of the nut against the fastened cbje t, the nut will remain fastened due tc the reactive tensicnmg thereof and the frictional grip on the thread cf the spindle on which the nut is threaded. In many situations, the object

to be fastened cannot rotate relative t: example, because it is keyed tc the spindle, so that tne possibility cf the nut unfastening by ιtse_ι s εi nincantly re uced anyway. However, the discovery mat little or low friction is required between the nut and the fastener object to keep the nut fastened, makes it desirable tc minimise sucr. friction so that more of the torque is available to be converted to hold-down pressure.

U.S. 4,969,788 discloses a nut with a pressure ring of the type having a spherically shaped undersurface for engagement with a complementary shaped depression in tne component to be fastened. The invention seeks to overcome problems associated with conventional slit pressure rings which are normally a separate component from the nut. A nut with a closed pressure ring connected theretc is provided, the means of connection permitting the nut and ring tc rotate relative to one another about the nut axis and tc shift relative to one another laterally cf the nut axis. The nut and the pressure ring have confronting pressure transmitting surfaces, and at least one of the pressure transmitting surfaces is provided with a plurality of recesses fcr holding lubricant. This can be achieved for example by shot peening the pressure transmitting surface. According to U.S. 4,969,78£. in this manner the shot peened pressure transmitting surface can be provided with a permanent lubricating film whereby friction between the nut and the pressure ring is not cf the same magnitude as with a slit pressure ring and a debasing of the hold-down torque during tightening of the bolt is reduced. The opposite confronting pressure transmitting surface is preferably finely turned or polished.

Presumably the lubricant employed is a liquid or viscous lubricant, for example grease, so that if the recesses in the shot peened surface are filled with the lubricant, as the nut and pressure ring are rotated relative to one another some of the lubricant in the recesses sticks to the confronting surface and is spread as a thin film between the pressure transmitting surfaces in known manner. This may prove satisfactory for a time, however after repeated use many cf the

recesses will be evacuated of lubricant and some of the lubricant will have been squeezed out from between the confronting surfaces so that little or no lubricant is left tc form the thin film therebetween. Furthermore, liquid and viscous lubricants are prone to dry out and solidify over time. Accordingly, the hold-down torque of the nut and pressure ring of U.S. 4,969,788 will be progressively debased during repeated tightening and loosening. More importantly, the liquid or viscous lubricant is unable to hold the two confronting surfaces fully apart so that there will always be a degree of metal to metal contact with the attendant friction therebetween. This problem is only exacerbated as the amount of lubricant between the pressure transmitting surfaces decreases over time. The present invention was developed with a view tc providing an improved fastener in which an increased proportion of the torque required to fasten an object can be converted tc pressure applied to the object, even during, and especially for, repeated tightening and loosening. Advantageously, the improved fastener can also be readily fastened by hand since less torque is required to achieve the same hold-down pressure as a conventional fastener thus the need for a tool to fasten or unfasten the fastener may be eliminated. The remainder of the specification will be directed primarily to one application of the invention, namely fastening a rotary tool such as a grinding wheel, circular saw, carving disc or router blade to a power tool, however it will be appreciated that the invention has much wider application, for example, in the automotive industry. A conventional clamp nut used for securing a grinding wheel to the spindle of an angle grinder is threaded through its central axis and cooperates with a washer-like backing plate which precedes the wheel onto the spindle. Shoulders provided on the spindle lock the backing plate to the spindle, and as the clamp nut is screwed onto the spindle it applies pressure to the wheel so that it is clamped against the backing plate and hence secured to the spindle. Conventionally, the friction grip of the plate on the grinding wheel when the nut

is tightened prevents the wheel from turning en the spindle. A spanner or similar tool may be used tc tighten the nut securely. Moreover, the clamp nut will also tighten spontaneously during use as the grinding wheel counter rotates relative to the direction of rotation of the spindle, when the wheel engages the work piece, so much so that it can be extremely difficult to remove the nut after use. Several improved types of fastener are known which are intended to eliminate the need for a special tool to loosen the fastener on the spindle and to make it easier to replace the grinder wheel or carving disc.

For example, AU 12247/88 (594557) by ROBERT BOSCH GmbH discloses a clamping device fcr axial clamping cf a disc onto a flange of a spindle of a power tool. The clamping device comprises a clamp nut which can be screwed cntc the spindle of a power tool, such as a portable grinder, and which supports a non-rotatable and axially movable clamp disc. The clamp disc engages the grinding wheel and is adapted to be loaded by the clamp nut with an axially directed compressive force and thus to press axially against the grinder wheel. An operating member is disposed between the clamp nut and the turning movement of the operating member axially releases the clamp disc from a clamped condition. Thus, the clamping device of AU12247/88 (594557) can facilitate easy release of the clamp nut by hand even when the latter is locked tight on the tool spindle. However, in certain circumstances a special tool may still be required, for example, when the clamping device is in a ruεted-on state or is used in the unlock position. Furthermore, the construction of the clamping device is extremely complicated with many moving parts and it is therefore expensive to manufacture. Moreover the operating member must protrude sufficiently outwards from the grinding wheel in order to be gripped by the operator' s hand and therefore presents an inconvenient obstruction during use. Also this clamping device is prone to spontaneously over¬ tighten with the turning of the grinding wheel and this is known to cause failure of the grinding wheel, apart from the usual problems of overtightening.

S MKAF.Y C"

: eci :ne cresent fastener m which significantly less of the torque is require; tc overcome friction when tightening and Iccsenmg tne 5 fastener.

Another object cf the present invention is to provide a gripping device which facilitates manual tightening and loosening of a fastener.

According to one aspect cf the present invention i; there is provided a fastener comprising: first and second components assemrler so so to c rctatεble w th respect to each other tc _^ t a ccmmcn ax s, saι„ first component having a first pressure transmitting surface adapted tc bear against an object to ce fastened and said 15 second component having a threaded port cn and peing adapted to apply an axially directed compressive force to press the first component against sa d object wnen a torque is applied to said second component; and, lubricating means provided between EΞI first anc Z εeccnd components to reduce friction therebetween whet one cf the components is rotated relative to the other ; whereby, in use- _* - said lubricating means can ensure that a significantly increased proportion cf tne torque applied tc εair seocnd component to fasten said object can be converted 5 to said compressive force transmitted through said first surface to said object.

Advantageously, said lubricating means comprises a solid dry lubricant, for example, a fluoropolymer plastic having a low coefficient of friction such as 0 polytetrafluoroethylene (PTFE) , commonly known by the trade names FLUON and TEFLON.

Preferably said solid dry lubricant ι_c m the form. cf a separate thin layer provided between facing surfaces cf said first and second components. In a preferred embodiment 5 said first and second components are substantially circular in snape, and typically comprise first and second disc-shaped

components respectively. The second disc-shaped component may be provided with a hub which is receive in an aperture provided in the first disc-shaped component whεrecy said first and second disc-shaped components share a common axis cf rotation. Advantageously said solid dry lubricant is m the form of a closed ring located concentrically between said disc¬ shaped components and lying immediately adjacent an cuter periphery of said hub.

Either one of the disc-shaped components may be provided with an annular receεε sized to receive said dry lubricant ring therein, and the other one cf the disc-shaped components may have a matching spigot adapted tc bear against the ring in said annular recess, wherein the height of said spigot relative to the depth cf said annular recess is selected so that the remainder of the substantially planar, facing surfaces of said components are normally separated by an air gap.

Advantageously said spigot and said annular recess each provide the only pressure transmitting surfaces on the facing surfaces of the first and second components.

According to another aspect cf the present invention there is provided a gripping device fcr manual tightening and/or loosening of a fastener, the device being provided integral to the fastener and comprising: a substantially planar member pivotaiiy connected to the fastener with the axis cf pivet lying m a plane substantially perpendicular to a direction of fastening cf the fastener, said member being capable of pivoting about said pivot axis to an upright position in which it lies substantially parallel to the direction of fastening whereby, in use, said member can be manually grasped to apply a torσue to the fastener.

Preferably said fastener is provided with a groove in which said pivotal connection of said planar member is located, wherein said torque can be transmitted to the fastener by means of said planar member engaging the sides of said groove.

Advantageously said axis of pivot passes through a

central axis of the fastener, said central axis :e:r; to said direction cf fastening. Typically said ras" tnreaded fastener and has a top portion ha ing ^ planar upper surface, said device being integral wit. portion. Typically said upper εurface is of circular said substantially planar member is m tne form of a flap or semi-circular shape, said pivot axis lying en a diametrical axis of said upper surface. Advantageously sair upper εurface is provided with a recessed portion adapte tc receive sard flap in a lowered position, in which it lies flat m a plane substantially perpendicular to the direction cf fastening.

Preferably said pivotal connection cf εaic flap s provided with biasing means fcr biasing said flap towards its lowered position.

BRIEF DESCRIPTION OF DRAWINGS

In order to facilitate a better unde εtandin: cf tne nature of the present invention several embodiments cf fastener according to the invention will now oe ceserired m detail, by way cf example only, wit;. re:er-_:. • t_ t;._ accompanying drawings, in which:

Figure 1 is a part-section viev. cf a grinte Λ.'.ee. on the spindle of an angle grinder power tool

Figure 2 is a section viev; through cne ertocd;~cnt or a fastener according tc the present invent- en, h t aan i., user to fasten the grinder wheel of Figure 1;

Figures 3 and 4 are a top perspective view and a bottom perspective view respectively cf a more preferred embodiment of the fastener, incorporating a gripping device also according to the present invention; and, Figure 5 is an exploded part section view cf the fastener of Figures 3 and 4;

Figure 6 is a part section viev: cf the fastener cf Figure 5 fitted to a grinder wheel; and,

Figure 7 is an enlargement cf a preferred form cf hinge connection for the flap on the fastener of Figures 3 tc β .

Referring tc Figure 1, a spindle 11 of an angle grinder iε illustrated having a threaded portion 12 and a shoulder 14 against which a washer-like backing plate 16 s seated. A grinder wheel or disc 18 s received en the bac ing plate 16. In the conventional means cf fastening the grinder wheel 18 to the spindle 1C, an appropriately shaped flange provided integral to a conventional clamping nut (not shown) , is screwed onto the threaded portion 12 of the spindle and applies pressure to the wheel 18 through the flange sc that the wheel is clamped against the backing plate 16 and hence secured to the spindle. A suitable tool must be used to tighten and loosen the clamp nut tc the spindle in order to secure and release the grinding wheel 18. Figure 2 illustrates one- embodiment of an improved fastener 20, according tc the present invention, in the form cf a clamping nut.

The fastener 20 comprises a first component 22 and a second component 24 assembled so as to be rotatabie with reεpect to each other about a common axis 2£, the first component 22 having a first pressure transmitting εurface 28 adapted to bear against the grinder wheel 18. The second component 24 has a threaded portion 30 for threadably engaging a threaded portion 12 cf the spindle 10, and is adapted tc transmit pressure through the first component 22 to fasten the grinder wheel to the spindle 10 when a torσue is applied to the second component 24. A lubricating means 32 is provided between the first and second components 22, 24 to substantially reduce friction therebetween when one of the components is rotated relative to the other.

In this embodiment, the lubricating means takes the form of three washerε 32 of εolid dry lubricant, for example, a fluoropolymer plastic having a low coefficient of friction such as PTFE, commonly known as TEFLON. In an alternative arrangement, the facing preεεure transmitting surfaces of the first and second components 22, 24 are each coated with teflon and then a further teflon washer is imposed therebetween. In a still further alternative arrangement, a single teflon washer 32 is provided and the facing pressure transmitting surfaces of the first and second components 22, 24 are bcth finally

turned or smoothly polished. In uεe, it is found traa seme cf the teflon material from the washer deposits onto tne component surfaces, thus further reducing friction therebetween. Typically, the first and second components are manufactured from stainless steel and the opposing pressure transmitting faces are provided with a close grain, smooth finish. A solid dry lubricant material such as teflon is particularly advantageous because it is lightweight, is chemically inert, is unaffected by changes in ambient temperature, including temperatures below freezing, can be of small dimensions, is ncn corrosive and unlike liquid and viscous lubricants is resiεtant to contamination or dehydration. The washers 32 ensure that a substantially increased proportion cf the tcrque applied tc the second component 24 is converted tc pressure transmitted through the εurface 28 of the first component 22 to the grinding wheel 18. The teflon washer also helpε prevent the grinding wheel from εpontaneouεly loosening when the tool is switched off and the spindle decelerates.

In this embodiment the first and second components 22, 24 are assembled with the first component 22 received on a hub 34 of the second component 24, and with the first component 22 effectively housed within the threaded component 24 but having the first pressure transmitting surface 28 exposed, so that only the surface 28 contacts the grinding wheel 18. The second component 24 is provided with a circumferential rim 36 having an inner circumferential lip 38 for engaging a corresponding outer circumferential lip 40 provided on the outer periphery of the first component 22. Thus, the teflon washer(ε) 32 are effectively sealed within the annular space between the first and second components 22, 24. The circumferential lips 38 and 40 are manufactured with close tolerances in order to inhibit the ingress of dust or other dirt particles into the space between the first and second components 22, 24. As the teflon washer(s) 32 is compressed between the first and second components 22, 24 when the fastener is tightened, the teflon material is effectively contained and prevented from spreading inwards by the hub 34, and from spreading outwards by the circumferential rim 36 cf

the second component.

The first and second components are secured in their assembled condition by a circlip 42 received on the huh 34 cf the threaded component 24. The first component 22 is alεc provided with a shoulder 44 which together with the hub 34 and circlip 42 is received within the central mounting hole of the grinding wheel 18. Due to the provision of the solid dry lubricant washer 32, as the threaded component 24 is screwed onto the spindle 10 of the angle grinder, significantly less torque is required to overcome face to face friction and accordingly a substantially increased proportion of the torσue is tranεmitted through the first component 22 to fasten the grinding wheel to the spindle. Indeed, less torque need be applied to the second component 24 in order to achieve adequate hold-down preεεure, εo that the fastener 20 can be tightened manually simply by grasping and turning the second component 24. For this purpoεe, the εecond component 24 may be provided with a suitable grip surface to facilitate manual tightening and loosening of the fastener 20. The outside diameter of the εecond component 24 may be increased to improve the mechanical advantage. A more preferred embodiment of the fastener according to the present invention will now be described with reference to Figureε 3 to 7.

The fastener 50 illustrated in Figures 3, 4, 5 and 6 comprises a first diεc-shaped component 52 having a first presεure transmitting surface 54 adapted tc bear against an object to be fastened. The faεtener 50 compriseε a second disc-shaped component 54 provided with a threaded portion in the form of a hub 56 received through a central aperture 58 of the second component 54. The first component 52 is also provided with a central aperture 60 having an inεide diameter slightly larger than the outside diameter of the hub 56. The firεt and second components 52, 54 are assembled on the hub 56 so as to be rotatable with reεpect to each other about a common axiε 61, and the second component 54 is locked to the hub 56 εo that when a torque iε applied to the second component as it is screwed onto a εpindle, compreεεive force is transmitted through the first component 52 in an axial direction to fasten

the chject against wnicn tne pressure transmitting surface 5u

or. the internal circumferential surface of tn aoerture 15 cf the seccn isc-shaped component 52. The splines 51 out into the external circumferential surface cf the nub 5c m order tc lock the two parts together in known manner. The diεc-shaped component 54 can be locked to the hub 56 in any known manner. An cuter ring 94 hclds the components together in their assembled condition. Lubricating means in the form cf a εclid dry lubricant is provided between the first and second components tc substantially reduce friction therebetween when one cf the components is rotated relative to the other. In this embodiment the solid dry lubricant is m tne form of a closed washer-like ring 62. Advantageously, the washer-like ring 62 is manufactured from a fluoropolymer plastic having a lew coefficient cf friction, such aε PTFE, commonly known as teflcn. The teflon washer 62 is located concentrically between the firεt and second components 52, 54 and lies immediately adjacent an outer periphery of the hub 56. The washer 62 iε cf minimum area in order to minimise the contact area between the facing pressure transmitting surfaces cf the first and second components and thus reduce friction therebetween. Fcr example, the teflon wash-Sr 62 in the preferred embodiment iε approximately 2mm wide and 0.5mm thick. The washer 62 iε preferably located immediately adjacent the. cuter periphery of the hub 56 in order to maximise the mechanical advantage obtained when a torque is applied to the relatively large diameter second diεc-shaped component 54. The first disc-εhaped component 52 iε provided with an annular recess 64 sized to receive the teflon waεher 62 therein. The annular receεε 64 opens out into the central aperture 6C of the firεt component 52. The second component 54 is provided with a matching spigct 66 adapted to bear againεt the waεher 62 in the annular receεε 64. The height of the spigot 66 relative to the depth of the annular recess 64 is selected εo that the remainder cf the εubεtantially planar facing surfaces cf the first and second components 52, 54 are

normally εeparated by an air gap. ή ^' er.ce, the spigct 66 and annular receεε 64 each provide the cr.ly pressure transmitting surfaces on the facing surfaces cf the first and εecond components, and thuε prevent metal tc metal contact between the first and εecond components 52, 54.

The annular recesε 64 together with the spigct 66 and the outer peripheral wall of the hub 56 together contain the teflon washer 62 and prevent spreading cf the solid lubricant material when a load is applied thereto. With the teflon washer 62 thuε contained, the εolid dry lubricant material can withεtand twice the normal load. The teflon waεher 62 also engages the outer peripheral wall cf the hub 56 to maintain a sealing relationship therebetween and thus prevent the entry of contaminants such as dust and ether particles. Furthermore. the washer 62 can also act aε a bearing tc inhibit metal to metal contact between the inner circumferential surface cf the aperture 58 and the outer peripheral wall cf the hub 56. The inεide diameter of the waεher 62 can be made equal to the outεide diameter of the hub and slightly larger than the inside diameter of the aperture 58 in the disc-shaped component 54, in order to prevent the component 54 moving laterally cf the common axis of the fastener. Both the components 52, 54, the hub 56 and the washer 62 are manufactured to close tolerances, typically to within five thousandth of an inch, to prevent contaminants from entering between the components. Obviously the annular recess 64 need not be provided immediately adjacent the hub 56, but may be spaced therefrom, but preferably not tc diεtant from the hub in order to retain the mechanical advantage. As illustrated in Figure 6 the first component 52 may be provided with an annular groove or receεs 68 (see Figure 6) intermediate the aperture 60 and the outer periphery of the first component 52 and adapted to receive a felt dust waεher 69 impregnated with a viscous lubricant, such aε grease, to exclude duεt. Figure 6 illustrates a part section view of the fastener asεembly received in an aperture 90 of a grinding wheel. The outer ring 94 is preεε fit onto a protruding portion of the hub 56 and holdε the firεt and second components

52, 54 together εc that they are free to rotate acout the ccmmon axis 61. A εeccnd teflcn waεner ray oe provide between the outer ring 94 and the firεt ccmpor.ent r_ rr. order t: minimise frietion therebetween if necessary. Advantageously the outside diameter cf the outer ring 94 ;: sited to fit m the aperture 90 of the grinding wheel and tn_e also serves to centre the wheel 92 on the spindle cf the tcol. r.er.ce, the outεide diameter of the hub 56 can be kept to a minimum. In Figure 6 it can also be seen most clearly hew tne rise-shaped components 52, 54 help to give the fastener C an overall low profile that only protrudes slightly aneve the central depression provided in the grinding wheel 91.

The εecond component 54 is preieracl-- manuf ctured from cloεe grained εtainleεε steel turnea or pclisr.ee tc a smooth finish, whereas the first component may be rιn„factureb from ordinary steel cr other suitable rigid material. Obviously the various componentε cf the fastener can be manufactured from any suitable materials, whether metal or ceramic or plastics as well as combinations thereof. As note above, some of the teflon material of the washer 62 will deposit in uεe on the adjacent pressure trrr.smittir._- surfaces of the annular recesε 64 and the spigot 61 ^* .:.„. further reducing any friction therebetween.

The operation cf the fastener 5C is similar tc that of the firεt embodiment described above. The second component 54 is screwed onto the spindle tc which it is to re fastened by means of the threaded hub 56 until the firεt pressure transmitting surface 53 of the first component 52 bears against the object to be fastened. The first component 52 thereafter remainε εubεtantially εtationery whilεt the second component 54 can be tightened to obtain the required tensicning on the spindle. Since the friction between the first and second components is minimised by the action cf the teflcn washer 62 subεtantially all of the torque applied tc the second component 54 iε converted to a hold-down preεsure applied tc the object to be fastened through the firεt component 52. This embodiment of the fastener 50 also incorporates a novel gripping device for easy gripping and manual tightening and/cr loosening cf the

fastener.

The gripping device 70 iε provided integral, to tne fastener 50 and comprises a substantially planar member in toe- form of a flap 72. The flap 72 iε pivctally connecter to the fastener with the axis cf pivot 74 lying in - a plane substantially perpendicular to a direction cf fastening cf the fastener. The flap 72 is capable of pivoting about the pivot axiε 74 to an upright poεition in which it lies substantially parallel to the direction of fastening and εubstantially perpendicular to the upper surface of the εecond component 54, εo that the flap 72 can be manually grasped to apply a torque to the second component 54. The flap 72 iε cf generally semi circular εhape in order to match the εhape cf the upper εurface cf the εecond component 54 of the faεtener. The upper surface of the second component 54 iε provided with a groove £ within which the pivotal connection of the flap 72 iε located so that a torque applied to the flap 72 can be transmitted tc the fastener by means of the flap 72 engaging the sides cf the groove 76. The groove 76 is provided in two sectionε lying on a diametrical axiε of the εecond component 54 and are shaped to receive a corresponding pair of projecting hinge portions 78 on the flap 72. The flap 72 iε provided with a cut-out section 80 shaped to accommodate the head 82 of the threaded hub 56 of the faεtener, when the flap 72 iε in its lowered poεition.

Advantageouεly, the upper εurface cf the εecond component 54 iε provided with a recessed portion 84 adapted to receive the flap 72 in its lowered position, in which it lieε flat in a plane substantially perpendicular to the direction of fastening. The hinge portions 78 on flap 72 project inwardly and are arranged to be held in the two sections of the groove 76 by means of an annular flange 86 provided on the head 82 of the threaded hub 56 in its assembled condition. Thuε, the groove 76, flange 86 and projecting hinge portions 78 of the flap 72 effectively provide a hinge connection for the gripping device 70. In an alternative arrangement the hinge portionε 78 project outwardly and the hub 56 is net provided aε a εeparate part from the disc-shaped component 54.

Advantageously the hinge connection is achieved simply by bending the projecting hinge portionε 78 cf the flap downwards to be received in the groove 76. This eliminates the need fcr a pivot pin. 5 As can be seen most clearly in Figure 7 the projecting hinge portions 78 of flap 72 also have an angled configuration, εo that the geometry of the hinge connection enables effectively double the thickness of the flap 72 at the hinge pivots. The angled configuration of projecting hinge 0 portion 78 ensureε that the projecting ear 79 of ^" the hinge portion iε free to pivot within the confines of the space defined by the groove 76 and the flange 86 without compromising the εtrength of the ear 79. The ear 79 iε provided with a rounded edge 81 to enable it to pivot freely within the 5 confined space beneath the flange 86 of the hub 56. In Figure 7 the flap is in its upright position. The flap is prevented from pivoting beyond its upright position by the projecting hinge portionε 78 engaging the upright wall 83 of the groove 76. Advantageously the height of the upright wall 83 is 0 increaεed in the region of the ear 79 by a raiεed annuluε 87 on the upper εurface of the εecond component 54, which matches a raiεed εection 88 of the flap 72. The raised section 88 of the flap 72 provides stiffening for the flap 72 in order to minimise bending when a torque is applied to the flap in its c upright position without compromising the overall low profile of the fastener.

The angled geometry of the projecting hinge portions 78 also provides a degree of resilience in the pivotal connection of the flap 72 εo that it iε held down in itε 0 lowered position. In addition, biasing means in the form of a leaf spring 87 may be provided between the flange 86 and the projecting portion 78 for biaεing the flap towardε itε lowered or upright position. The biasing of the flap in its lowered position is preferably sufficient to hold the flap 72 down 5 against its own weight, so that even if the fastener 50 is turned upside down the flap remains closed. However, the flap 72 can be easily lifted with the finger against the action of the leaf spring. For this purpose, the outer diameter of the

iε preferably slightly larger than the outer diameter of the second component 54 εc that the flap marginally overlaps the second component 54 to facilitate lifting. In itε upright poεition, the angled hinge portions 78 ensures that the flap 72 is net quite perpendicular to the upper face cf the component 54 so that the flap will close by itself due to centrifugal force when rotated. Preferably the cut-out section 80 in the flap 72 is not sufficiently large to enable a finger to be caught therein, but is large enough to receive the shaft of, for example, a screw driver to provide additional leverage if necessary.

It will be appreciated that the configuration of the flap 72 provides maximum leverage on the fastener 50 since it takes maximum advantage of the larger diameter of the second component 54. The hinge connection of the flap 72 iε provided in the diametrical groove 76 and hence the groove 76 carries the load when a torque iε applied to the gripping device, rather than the pivotal connection itself. The illustrated embodiment of the gripping device 70 iε particularly advantageous since in the lowered position of the flap 72 it maintains the low profile of the fastener 50. Furthermore, since the gripping device iε provided integral with the faεtener 50 there iε no poεsibility of the gripping device becoming misplaced, and thus having the inconvenience of a user having to locate the gripping device before being able to loosen the fastener. Not having to use a tool eliminates the danger of injury in the event the power tool iε inadvertently εwitched ON. To loosen or tighten the faεtener, the uεer εi ply liftε the flap 72 and applieε a torque thereto in the appropriate direction to looεen or tighten the faεtener.

Now that preferred embodi entε of the faεtener and a gripping device according ^' to the invention have been deεcribed in detail, it will be apparent that both the faεtener and the gripping device provide εignificant advantages over and improvementε to conventional fastenerε. Moεt importantly, the proviεion of a solid dry lubricant between the first and second components ensures that a significantly increased proportion cf the torque applied to the fastener is converted to a hold-

down pressure app-ier to tne object to be fastener. The preferred embodiment cf the fastener is particularly advantageous in itε application to fastening of a grinder- wheel, carving disc or circular sav-- blade to a power tocl, since it facilitateε easy manual securing and releasing cf the disc or blade to/from the spindle of the power tool. As with a conventional clamp nut, the faεtener cf the invention can εelf-tighten spontaneously on the spindle when the power tool iε switched ON, however the design cf the fastener advantageously prevents overtightening. At a certain hold-down pressure (tightness) the friction between the thread on the threaded component and the thread en the spindle will exceed the friction between the threaded component and the first component (minimised due to the dry lubricant waεner, . At that presεure (or greater, the threader component will net tighten any further aε the first component will turn by itself with the, for example, grinding wheel, without the threaded component turning relative to the grinding wheel. Hence, the threaded component will never overtighten and can still be released manually without difficulty. Likewise, when the spindle decelerates after the tool iε switched OFF, the same effect prevents the fastener from εpcntanecuεly iocεening, and increaεeε the safety of the powe -tool. The same "clutch" effect operates when the- grinding wheel engages a wcrk piece in use; the first component can accommodate a fraction of a revolution of slippage tc reduce the shock en the gear box of the power tool. The teflon washer also absorbs a degree of vibration and this also helpε to inhibit looεening of the faεtener. Furthermore, the proviεion of a gripping device typically in the form of flap 72 provideε an extremely effective meanε of manually applying a torque to the fastener.

Numerous variations and modifications will suggeεt themεelveε to perεonε εkilled in the appropriate arts, other than those already described, without departing from the basic inventive conceptε. For example, although both the illuεtrated embodiments employ a hollow threaded hub cr hub for screw- attachment to a spindle, clearly the hub cr hub could be replaced with a threaded spindle provided integral tc cr locked

to the εecond component 54. Furthermore, although in the preferred embodiment the firεt and second components are diεc- shaped in order to give the fastener 5C an overall low profile so that it can be accommodated in the central depression cf a grinding wheel, this is by no means essential to the present invention. The faεtener may be of any deεired shape, fcr example, the second component 54 may take the form of a conventional nut suitably modified en its pressure transmitting surface to accommodate the first component and the solid dry lubricant therebetween. The first component and the teflon washer may also be configured to fit within the securing nut of the kind used for εecuring a tool employing a Kcrεe-taperer chuck, for example, aε on straight shaft grinders and metal milling machines. Furthermore, the faεtener need net have a gripping device in the form of a flap, but may instead have a larger profile and be provided with a grip surface. Fcr similar reasons, the flap 72 of the gripping device need not be of semi-circular εhape, but may be configured to match the shape of the upper εurface of any faεtener to which it iε applied.

The εolid dry lubricant need not be in the form, of a washer-like closed ring, but may be of any suitable shape cr configuration, for example, in the form of radially extending ribε located in matching receεεeε. Furthermore, the lubricating eanε need not be provided as a separate integer between facing surfaceε of the first and εecond components, but may be provided integral to either one or both of the facing surfaces of the first and second components, for example, by manufacturing the component(s) from a εuitable plaεticε material having a low coefficient of friction. Likewise, the annular spigot in the preferred embodiment may be replaced with a washer of suitably hard material, for example, stainless steel which may be used with two or more teflon washerε to eliminate the need for a smooth bearing εurface on either the firεt or second component.

It will be obviouε that the gripping device 70 has much wider application to faεtenerε other than the fastener according to the present invention. For example, the gripping

device 70 may also be provided integral to tne read of conventional screw cr bolt or a drill chuc,-. to facilitate manual fastening or turning cf the same. All ε .cr. variation: and modifications are tc be considered within tne scope or th- present invention the nature of which is tc be determined fro: the forgoing description and the appended claims.