AU665820B2 - A press-in cover for the drive recess of a screw head - Google Patents

Description

v6 658 O2 0 fP00/011 AUSTRALIAegulation 3.2 Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

NOTICE

1. The specification should describe the invention in full and the best method of performing it known to the applicant.

2. The specification should be typed on as many sheets of good quality A4 International size paper as are necessary and inserted inside this form.

o. 3. The claims defining the invention must start on a new page. If there is *insufficient space on this form for the claims, use separate sheets of paper.

The words 'The claims defining the invention are as follows" should appear before claim 1. After the claims the date and the name of the applicant should appear in block letters.

4. This form must be accompanied by a true and exact copy of the description, claims and drawings (if any) and an additional copy of the claims.

(see Pamphlets explaining formal requirements of specifications and drawings) TO BE COMPLETED BY APPLICANT I ::ame of Applicant: SHIRLEY M LISTR-PUCHY a e l p t. t. a inventor.):. David Peter William PUCHY (Deceased) A ctu a l Inv e nto rts): HA JL LI/DA-S Addess for Service: 44 ASHLEY STREET. HORNSBY N.S.W. 2077, AUSTRALIA I o Invention Title: A PRESS-IN COVER FOR THE DRIVE RECESS OF A SCREW HEAD PLP'166 Details of A ssociated Provisional Applications: Nos: The following statement Is a full description of this invention, Including the best .method of performing it known to me:- A PRESS-IN COVER FOR THE DRIVE RECESS OF A SCREW HEAD The present invention relates generally to decoratively concealing, press-in covers for the drive recess in the heads of screw fasteners and in particular to improved gripping means whereby the covers are releaseably retained in place.

BACKGROUND TO THE INVENTION The cover has been particularly designed for use in drive recesses of crucifix form. There are two common forms 10 of crucifix driving recesses which are known by the trade marks PHILLIPS and POZIDRIV. Hereinafter reference to 'cross-head screws' is to be taken as reference to screws with crucifix driving recesses of the PHILLIPS or POZIDRIV form. It will be appreciated that the work loading upon the ~15 punch tools, which form the driving recesses in the screw heads during manufacturing, is very high indeed. The operation involves "plastic" displacement (cold flow) as a hardened steel punch is forced into the relatively softer steel in the screw blank.

20 In order to provide manufacturers with an economical scale of production from each punch tool, broad tolerances are allowed for the formed driving recesses. Limits to these tolerances are governed only by regard to the effective operation of the driving tool (screw driver) which has to fit the driving recess in complementary fashion, when used to fix the screw.

The width of the wing portion of a No. 2 size crucifix driving recess, for example, may in practice, vary by 0.01 inches (0.25mm). However, a feature of the plastic moulding process by which the press-in 2 covers are produced, is an ability to reproduce components to close tolerances ie. within 0.001 to 0.002 inches (0.025 to 0.05mm) depending upon moulding conditions and materials in use.

It can be seen then, that there occurs during production runs, each of screws and press-in covers, a diverse discrepancy in sizing between dimensions of the driving recess which may be formed in the cold headed steel screws, and the attachment, or gripping means of the press-in cover substratums.

It is this discrepancy in sizing, which when taken into consideration, together with the impeding nature of the generally converging, smooth, hard surfaces of crucifix driving recesses, and the oeeo relatively low frictional properties of the oe thermoplastic polymers used for the cover, which constitute such a difficult assignment for designers of these covers.

However, when coupled with the further and by far, the most significvnt complication in the whole design equation, namely that of having in common usage, two standard recess configurations of diverse shape and dimensions, (Phillips and Fozidriv), the complexities 0of the design are greatly magnified.

It is hardly surprising therefore, that press-in covers have in the past, been specifically designed for use with either Phillips or Pozidriv recesses.

3 Since no undercut or other irregularity exists within the driving recess, to which some form of positive attachment may be made, it is both logical and self evident that all such covers are compelled to rely upon the generation of some form of frictional grip, for attachment.

The numerous substrate designs of -the many prior art covers which, hitherto, have been advanced, have, so far as the inventor is aware, been of two basic types; round, cylindrically or conically shaped stems, or alternatively, the so called 'star' configurations.

Whilst the round, cylindrical and conical substrate stems are self explanatory, the 'star' shaped substrate is not. It basically consists of four wing .:portions, approximating the inverse shape of the driving recess wing portions, raiiating outwardly at deqrees to each other from a central stem portion; the stem portion extends perpendicularly from the underside of the crown portion of the press-in cover. Sometimes the wing portions are split radially, so that each such portion becomes two substantially narrower portions.

Both substrate types rely upon a light to heavy *"interference fit with the top tolerance dimensions of the corresponding portion of the driving recess into which they are intended to engage, in order to produce a frictional grip with the drive recess.

Many substrate forms are provided with integral bearing strips or humps, upon the substratum, for 4 engaging the recess. The purpose of these is to compensate for the manufacturing tolerance discrepancies previously expounded, by readily displacing to conform to the recess size, when engaged therein.

Before examining the effectiveness of this design feature, it is first necessary to understand both the effects and the importance of matching the engagement method incorporated in the substrate design, to a suitable thermoplastic polymer, as the multitude of such materials differ greatly in their characteristics and properties.

For example, some thermoplastics with good resiliency (which could reasonably be considered a desirable characteristic for these types of applications) generally have poor frictional properties, whereas, other polymers, having better frictional properties, do not readily displace or Sdeform under load, or else, lack the resiliency characteristic needed to maintain the loading (force) upon the polymer surfaces in contact with the driving recess surfaces.

A measure of resiliency is an essential requirement of achieving optimum frictional grip of the substrate with the driving recess, since parameters governing the effects of friction are: Load (force) x Area (of contact surfaces) x Coefficient of Friction (between surfaces in contact).

Some polymers have high resilience, wherein they behave in a similar way to rubber, in that displacement in consequence of an applied load, consequentially is distributed substantially uniformly through the affected region of material. This group of thermoplastics have dominant 'memory' characteristics which program them for relatively quick recovery to their original form, following deformation within elastic limits. Permanent deformation is characterised '0 by high loadings, to cause the considerable displacement needed to exceed their elastic limits.

Once the elastic limit is exceeded, resistance to continued load application greatly diminishes as too, does resistance to further deformation.

Whereas, the less pronounced resilience of another group of polymers, is characterised by the progressive effect or reaction of the material to loads applied thereto, wherein zones or layers, beginning with those closest in proximity to the points of load *e 20 application, react in order to balance the applied load by virtue of the energy which is absorbed by the progressive deformation and/or displacement of the zones beyond the elastic limits of the materials, until equilibrium is restored between the dissipaiAng load 0e "and the deforming materia..

Any attempt upon this polymer group, to increase the applied load upon surfaces in contact, for example: by wedging the substrate deeper into the converging confines of the driving recess or by 6 providing wider interference fits, is substantially negated by the effects of the progressive absorption of the increased loads by the zones or layers. It is to be understood that the circumstances described herein, are always dependent upon there being adequate volumetric capacity within oi access without the driving recess to accommodate the permanently displaced material.

It can be seen hereby, this group of polymers provide a substantially constant reactionary load characteristic irrespective of the degree of deformation reached, providing the elastic limit is not exceeded throughout the load-affected region, as thereafter, this group behaves in much the same manner as the former group.

S. A most important derivative of this constant-load peculiarity is that it provides a method of achieving a substantially constant frictional grip between the substratum of a press-in cover and the driving recess of a fixed screw, provided some displacement of substratum material is effected. In consequence thereof, a reliable grip in the recess is effected regardless of the height of the fixed screw head above or below the work surface, within practical limits. The height of the fixed screw head varies in practice, according to the skill of the fixer who operates the powerdriver and in accordance with the variable nature of workpiece materials. In -7 particleboards, for example, the practical variation is in the range of from 0.5mm below to 0.5mm above the workpiece surface, and hitherto, performance and effectiveness of most of the prior art covers have very much been compromised by this discrepancy. The notable exception being a long stemmed cover with a spigoted connection to a specialised screw, which is described in more detail below.

A third group of thermoplastic polymers exists, in which the materials behave under load, in a somewhat similar manner to thermosetting materials. These generally, exhibit increased hardness properties, but tend to be relatively brittle and cr[,mbly under excessive load. They have very low resilience and poor **elastic properties, though some do exhibit better than average frictional properties. Generally, this group is considered unsuitable for the present application.

In the substratum configuration employing 'bearing' strips or humps to compensate for the tolerance variations, the grip generated will vary according to the choice of polymer, surface coptact areas achieved and the applied load. In these cases, o 0 it is apparent that even when maximum displacement or deformation of these strips or humps occurs, and even allowing that the frictional grip between the strips or humps and the surfaces with which they are in contact, is of a high order of magnitude, the fact remains that the contact surface area is very small resulting in a very low overall frictional value. In reality their 8 performance lacks uniformity and therefore dependability, to provide secure concealment of the fixed screw.

The only design known to the inventor, which provides consistently satisfactory performance, is the previously mentioned design in which the dependent substratum is a relatively long, round stem, which spigots into a hole drilled axially down into the shank of the screw, through the bottom of the driving recess.

Because the hole is produced by drilling, closer tolerancing of its diameter during a production run, is possible and the elongated stem substratum of the press-in cover is sized to be a lightr interference fit into it. A secure and reliable mating of the two components is achieved as a result of the relatively large area of contact between them.

The major drawback of this arrangement is of a commercial nature. The added cost of producing the drilled holes in the screws, prices them well above that of competitive fasteners (more than 50% more expensive). In the very competitive fastener field this price disadvantage is sufficient to limit its commercial use.

\In order to provide a means of improved frictional grip between a substratum and a driving recess, a study of the available useful contact surface areas of both cross- hecc Sr_, cA%'i% recesses is 1Tnecessary.

Such studies highlight the reason why round, cylindrical or conical stems, spigoted into the central apertures of cross-head screw driving recesses provide inadequate grip.

At best, they make only limited contact along approximately length of edge surfaces of the cross-head screw driving recesses and eight such edge surfaces in Pozidriv. At no time do these substrates make any significant contact with flat surfaces, owing to the fact that all such surfaces, which define the central aperture of the driving recess, are angled away from the substantially round surface area of the inserted substratum.

The 'star' configured substratum relies for Grip, upon surfaces of the wing portions of the substrate contacting 15 corresponding surfaces in the recess. Alternatively, it relies upon the above in combination with the edge surface contact upon its central stem portion, described in the I foregoing paragraph. The substratum wing portions are almost always sized towards or above the top tolerance dimension of 20 the corresponding wing portion of the driving recess, such that an interference fit is created when the substi:atum is pressed or hammered into the driving recess.

In practice, they will not fit recesses towards the lower end of the tolerance scale, the overlapping material 25 of the substratum being either sheared against the edge of the recess, or alternatively, caused to displace against the top edge of the recess. In both cases, the excess material, builds up under the crown of the cover and can prevent the substratum from penetrating deeply enough into the driving recess. At best, they provide irregular grip and therefore unreliable concealment of the fastener.

Neither of these basic attachment configurations tahes advantage of the major bearing areas in the driving recesses of both cross-head screws which is provided by the surfaces defining their central apertures.

This invention is addressed to overcoming the above detailed deficiencies, obstacles and drawbacks of the prior art products.

SUMMARY OF THIS INVENTION The purpose of the present invention is to provide a new and novel substrate gripping mean.s, being dependent from the decorative crown portion of a low cost, press-in cover for concealing screw fastenings, in which provision is made, not only to compensate for the size variations arising out of the manufacturing tolerances applying to the crucifix shaped driving r t" 'i ,-a (i r ii 8 recesses resid in the heads of the screw fastenings, but also to provide a single product which is equally adaptable and dependable, to provide secure attachment within the driving recesses of both cross- heocAo In order to produce improved grip, optimum values must be provided for the previously stated three parameters which govern the effects of friction: firstly, by providing increased areas of the surfaces in contact between the substrate gripping mea s and the driving recess; secondly, by choosing a polymer capable of providing adequately high resistance in reaction to displacement loads, and thirdly, by choosing a polymer which combines optimal frictional properties with the abovestated high resistance property.

The choice of such material comes from the .0o. *second polymer group discussed in the foregoing text.

Two such materials which have proved satisfactory in practice, are Styrene and ABS. Styrene is possibly more suitable from a commercial viewpoint; being inexpensive, readily available, blends easily with colourants, is easily moulded and may be modified with microscopic spheres of rubberised compound, which both assists its resilience and impact strength, as well as enhancing its frictional properties.

As previously stated, the major useable surface areas for attaching a gripping means within a crucifix fR driving recess, occurs in the central aperture of the drive recess. It is to this region that the gripping means of this invention is directed. The wing portions of the driving recesses are, to a large extent, excluded. This is partly because they have the least factors in common to both recesses, so far as providing gripping surfaces for a common element is concerned, but primarily for the reason that the surfaces thereof are frequently damaged and distorted by the camming-out effects of the powerdriver bits used to fix the screws, resulting in burrs and dags protruding therefrom, which hinder engagement of the gripping means with the driving recesses.

The central apertures of both known cross-head screw driving recesses on the other hand, although distinctly 15 different are nevertheless, surprisingly close dimensionally, and have similar contact surface areas, similar volumetric :capacity and similar angles of convergence of the contact surfaces.

a a 13 GENERAL STATEMENT OF INVENTION Broadly stated the invention can be said to provide a press-in cover for forced insertion into a drive recess in a screw head where it is resiliently retained, where said cover is made of a resiliently deformable mate-.ial and comprises a head, an elongated substratum integral with the head and having a central longitudinal axis which lies normal to an underface of the head, said substraturm includes a body which tapers and is largest adjacent said head and includes four primary wings extending the length of the body and equally angularly spaced around said substratum axis, each primary wing has an outer face with a longitudinally extending valley in the outer face between two wing edges, a secondary wing between adjacent primary wings and extending .in the length direction of the body and spaced from the adjacent primary wings, each secondary wing has an outer face with a longitudinally extending valley in the outer face between two wing edges, the valleys in the outer faces of the 20 primary and secondary wings allow 4 4 44 1 *a L resilient deflection of the wing edges when said substratum is forceably inserted in a drive recess; in a screw head.

The invtntion in a specific form can be said to provide a press-in cover for an inwardly tapering crucifix shap. drive recess in a screw head, where the drive recess has a centre zone with a central axis from which radiates four drive slots each with two sides and an end, the drive slots are equally angularly spaced around the said central axis and between adjacent drive slots there is a pair of inwardly convergent bearing surfaces: said cover is made of a resiliently deformable material and comprises a head, an elongated substratum integral with the head and having a central longitudinal axis which lies normal to an underface of the head, said substratum includes a body which tapers and is largest adjacent said head and includes four drive slot engaging primary wings extending the length S. of the body and equally angularly spaced around said S* 20 substratum axis, each wing has an outer face with a longitudinally extending valley in the outer face between two wing edges, said valleys allowing the oIoo distance between the wing edges to be decreased by forced wedging engagement of the wing edges with the sides of the drive slots of a crucifix drive recess, a secondary wing between adjacent primary wings and extending in the length direction of the body and spaced from the adjacent primary wings by slots, each secondary wing has an outer face with a longitudinally extending valley in the outer face between two wing edges, the valleys of the secondary wings allowing the distance between the wing edges of the secondary wings to be increased by forced wedging engage'int of the secondary wing edges against inwardly convergent bearing surfaces in a crucifix drive recess.

PREFERRED EMBODIMENT DESCRIPTION The following is a description of two embodiments of this invention. One embodiment has particular reference to the accompanying drawing figures 1 5 which illustrate in plan view, the step by step basic construction of the substratum cross-sectional shape for a press-in cover according to the invention, and wherAin: 1 shows the rectangular crucial elements .of this construction perpendicularly intersecting each other symmetrically, to form radial wing portions; a a Fig. 2 shows the addition of fillet portions in a. a.

e S 20 each corner of the structure to conjoin with side surfaces of adjacent wing portions; Fig. 3 shows the subdivision of each fillet *9*a portion by a shallow narrow groove, as forms part of the substratum for one embodiment of the invention; Fig. 4 shows the subdivision of each fillet portion from its conjoining relationship with each respective wing portion by a deeper narrow end groove; /Fig. 5 shows each end surface of the wing 16 portions grooved out in a vee configuration to provide a valley between two wing edges; Fig 6 is an enlarged Plan View from the underside of the structure of one embodiment of this invention; Fig 7 is an Elevational View of Fig 6; Fig 8 is a partially sectioned, scrap Elevational View of Fig 6 viewed at 45 degrees to that shown in Fig 7; Fig 9 is an enlarged Plan View of a No. 2 size of one form of cross-head screw driving recess, drawn to its minimum tolerance dimensions; Fig 10 is a Sectional Elevation View of the No. 2 size recess of Fig 9, through the plane AA to show areas defining usable 15 contact surfaces within the central aperture portion of the drive recess; Fig 11 is another Sectional Elevational View of the No.

2 size recess of Fig 9, viewed at 45 degrees to that shown in Fig 10 and showing the cross sectional shape of its 20 central aperture portion of the drive recess; Fig 12 is an enlarged Plan View of a No. 2 size of another form of cross-head screw driving recess, drawn to its minimum tolerance dimensions; Fig 13 is a Sectional Elevational view of the No. 2 size recess of Fig 12, through the plane BB to show areas defining usable contact surfaces within the central aperture portion of the drive recess; 17 Fig 14 is another Sectional Elevational view of the No.

2 size recess of Fig 12, viewed at 45 degrees to that shown in Fig 13, to show the cross sectional shape of its central aperture portion of the drive recess and having the elevational section of Fig 11 overlaid in chain dotted lines in order to compare shape and size differences between the central aperture portions of the illustrated forms of thd driving recessese Fig 15 is the Plan View of Fig 9, recess overlaying the Plan View of Fig 12 recess, both drawn to minimum tolerance dimensions, to illustrate the closeness in size of their respective central aperture portions, regardless of their different configurations; i..i 15 Fig 16 is a cross sectional Plan View of the dependent substratum structure of this invention at its juncture with 0 the crown portion, thereby to illustrate the nature and extent of its overlap of the central aperture portions of a Fig 9 recess; 20 Fig 17 is a cross sectional Plan View of the depen-,.; w substratum structure of this invention at its juncture wi' Z the crown portion, as in Fig 16 but this time, illustrating the nature and extent of its partial overlap of the Fig 12 ocentral aperture portion; 25 Fig 18 is an enlarged cross sectional Plan View of the "dependent substratum structure of this invention viewed through the plane C-C of Fig 7, overlaying a Fig 9 recess (shown in chaindotted lines) to illustrate the reduced dimensions at the lower r8 extremities of the substratum bearing areas, permitting location within the z 9 recess central aperture, preparatory to forced engagement therein. It will be apparent that the lower extremities will in consequence, also locate within the central aperture of a recess; Fig.19 is a sectional view through a fitted substratum along a plane coincidental with the maximum opening of a F recess, showing distortion of substratum bearing surfaces to conform substantially to the recess central aperture configuration; is a further sectional view through a fitted substratum along a plane coincidental with the maximum opening of a FL l- recess, showing slightly less distortion than occurs in Fig. 19, but again, substratum bearing surfaces conform substantially to the central aperture configuration of the drive recess.

Fig.21 is an enlarged Plan View from the underside of the structure of a second and preferred 20 embodiment of this invention, which is very similar to the first embodiment; and Fig. 22 is an Elevational View of Fig. 21; In the Figs. 6 to 8, it can be seen that the components of this invention consist of two basic portions, a crown or head portion 1 and a dependent substrate portion 2. The upper surface of the crown portion 1 is purely aesthetic in purpose, serving to conceal or decorate the exposed portion of the head of a fixed screw fastener and therefore, may be any shape, size or configuration considered suitable for the purpose. The undersurface of the head 1 has a preferred configuration as will be described, later.

The dependent substratum portion 2 is a structure intended to perform a specific function which is to grip in the socket of the screw head to hold the cover head 1 in a covering position over the screw head. The substratum comprises two portions consisting of an upper portion 3 and a conical, reduced lower portion 4.

The upper portion 3 is characterised by havring its uppermost extremity 5, integral with the underside of g the crown portion 1 and its lowermost extremity or free end 6, coincidental with a horizontal plane 7. The plane 7 delineates the junction of the upper portion 3 with the reduced lower portion 4 of the substratum 2.

The portion 4 is a preferred and not an essential part of the substratum as will be clear from later description.

"'.The upper portion of the body 3 has a central axis and is constructed in the basic configuration of a crucifix prism, wherein two identical members intersect symmetrically with respect to the axis, and whereby the portions radiating outwardly therefrom, are referred to as wing members 8 (Fig. The wing members form between their adjacent sides 9, nooks 10, each nook being occupied by a fillet portion 11 (Fig. 2).

S7 The fillet portions 11 are centrally provided with a groove 13 (Fig The included angle of convergence of diametrically opposed pairs of the surfaces 12, approximates the included angle of convergence of the diametrically opposed inwardly convergent bearing surface pairs 14/15, defining the respective central aperture portions 16 and 17, of a cross-head screw first form aperture 18 and a cross-head screw second form aperture 19 respectively, as seen particularly in the Figs 11 and 14.

In both instances the drive apertures 18 and 19 have a centre zone (16, 17) with a central axis from which radiates four drive slots each with two sides and an end, the drive slots are equally angularly spaced around the said central axis and between adjacent drive slots there is a pair of inwardly 15 convergent bearing surfaces 14 and 19.

The continuity of the surface union of the fillet portions 11 with respective adjacent sides 9 of the primary

S.

wings 8, is interrupted by the intersection of further grooves 20, placed axially at intervals in the substratum 20 structure, and extending at least the axial length of the fillet portions 11. The grooves 20 are disposed in opposing pairs to concurrently produce partial undercuts into the 0 primary wings 8 and behind the fillet portions 11 thereby o forming secondary wings 8a between the primary wings.

25 When viewed in elevation, the secondary wing edges 21, defined by the intersection of the grooves 20 with the fillet portions 11, and sides 9, taper downwardly, thereby to regulate surfaces 12 of the fillet portions 11, to proportions which when fitted therewith, wil' complement corresponding inwardly convergent surfaces 14/15 in the respective central aperture portions 16/17 of a recess 18 and A recess 19.

The outer face 22 (Fig. 1) of each primary wing member 8 is provided with a valley like groove 23 of Vee shape (Fig. 5) between two wing edges. The valleys extend along the primary wings and are terminated, substantially towards the lower extremity thereof, by an obtusely angled cutting plane which forms the chamfered edge surface 24 (Fig. The opposed sides 9 of each wing member 8 may be faceted at their lower ends to provide the further plane surfaces 25, which converge downwardly substantially to a point intersection 26 with the chamfered edge surface 24 and the lower boundary plane 27 of the conical, reduced lower portion 4 of the substratum 2.

2o The substratum 2 may be cored out by provision of a cylindrical or suitably configured opening 28 extending perpendicularly inwardly from the surface of the boundary plane 27, the size and depth thereof serving to provide substantially uniform wall thicknesses, thereby to help prevent a 'sink' depression occurring in the crown portion 1 adjacent the substratum 2 of the moulded component.

The embodiment illustrated in Figs.21 and 22 is the presently preferred embodiment. It has the basic 2- elements of the embodiment previously described. One variation is the provision of a faceted fillE. (shown dotted between two wing members 8 in Fig.2) in place of the curved fillet 11. This results in the outer faces of the secondary wings between the wing edges 21 being of Vee shape rather than the curved shape with the central groove 13 of the first embodiment.

The manner of resilient engagement of the wings of the press-in cover in the crucifix drive recess of a screw is as shown in Figs.19 and 20 for both of the embodiments herein disclosed. The valleys in the outer faces of tne primary and secondary wings function, as will be seen from Figs.19 and 20, so that the wings edges are resiliently deflected from their base positions.

Specifically, the valleys in the outer faces of the primary wing allow the distance between the wing edges of the primary wings to be decreased by forced wedging engagement of the wing edges with the sides of the d-'.ve slots of a crucifix screw head drive recess and the valleys in the outer faces of the secondary 0 wings allow the distance between the wing edges of the secondary wings to be increased by forced wedging engagement of the secondary wing edges against the radially inwardly convergent bearing surfaces 14,15.

The result is a resilient frictional contact between the wing edges and the sides of the slots and the surfaces 14,15 sufficient to firmly secure the press-in 3cover in place anchored only by the said frictionaJ contact.

It is to be noteu in both embodiments the head 1 of the cover has a curved top and in the first embodiment (Fig.7) the terminal peripheral edge of the head is a surface whereas the head of the second embodiment (see Fig.21) is an edge. The undersurface of both forms of head is dished providing the underface with which the upper end of tht. ibstratum is joined and with respect to which the central axis of the substratum is normal. The peripheral under edge of each head occupies a plane :paced from the plane of the underface, this arrangement ensures that when the cover is mounted in a sc~.ew the under edge of the head 1 wi)1.

engage the surface surrounding the screw head as the substratum iF forced into the drive recess in the screw head. The edge of the head by its shape, particularly when of the form shown in Fig.21, provides sufficient flexibility to ensure a neat -inish with the head edge 20 firmly contacting the surface around the screw when the cover substratum is forced fully into the screw head drive recess. The dishing of the head also allows room for any possible sheared or displaced material from the substrate as it is forced into the drive recess in the screw head. In addition the dishing allows (within limits) for variations in the height of the outer end of the screw head above the work surface and room for any burring of the drive recess resulting from the power driving devices.

24. The orienting feature of the cover involving the substratum portion 4 and the chamfered ends of the primary wings as indicated 24 and 25 are preferred features and facilitate the correct alignment of the primary wings with the limbs of the crucifix drive recess in the screw head.

Whilst it is anticipated that modification or alteration of the features herein disclosed in the description of the two preferred embodiments is possible to those skilled in the art, it is not intended that the scope of this invention should be limited by the foregoing descriptions, or the delineations and proportions seen in the accompanying drawing figures. Whereas the edge surface grooves (valleys between wing edges) for example, are specified as vee shaped, it is conceded that shaped grooves would function equally well. Nor is the invention confined to channel shaped depressions to form the undercuts. These may be shaped in any desired manner, 20 without detracting from their purpose or function, 0e20 a a Nor is it necessary for the fillet portion bearing surfaces to be radiused; they may be gusseted, faceted or irregular, though preferably retaining a measure of concavity, without deviating from the disclosed principles of this invention.

Whilst the cover hereinbefore described has been particularly described with reference to a Acrucifix drive recess its form allows it to be used in other drive recess configurations. In particular, recesses of suitable size where the drive recess or central aperture of the drive recess conforms substantially with the substratum.

The invention in its broadest forms is such as to fall within the terms of the following claims.

.9 9 9

Claims (4)

1. A press in cvrcr for foroed incortion into a driv recess in a screw head where it is resili tly retained, where said cover is made of a res' iently deformable material and comprises a head, elongated substratum integral with the head and ving a central longitudinal axis which lies normal o an underface of the head, said substratum inclu s a body which tapers and is largest adjacent s d head and includes a plurality of spaced apart ings extending the length of the body and equal angularly spaced around said substratum axis, each wing has an outer face with a longitudinall extending valley in the outer face between tw wing edges, the valleys in the outer faces of the/wings allow resilient deflection of the wing ed s when said substratum is forceably inserted in a ssrivz rzcccs in a crow hoad. oe s I. A press-in cover for forced insertion into a drive recess in a screw head where it is resiliently retained, where said cover is inade of a resiliently defornable material and comprises a head, an elongated substratum integral with the head and having a central longitudinal axis which lies normal to an underface of the head, said substratum includes a body which tapers and is largest adjacent said head and includes four gprimary wings extending the length of the body and I equally angularly spaced around said substratum axis, -21- each primary wing has an outer face with a longitudinally extending valley in the outer face between two wing edges, a secondary wing between adjacent primary wings and extending in the length direction of the body and spaced from the adjacent primary wings, each secondary wing has an outer face with a longitudinally extending valley in the outer face between two wing edges, the valleys in the outer faces of the primary and secondary wings allow resilient deflection of the wing edges when said substratum is forceably inserted in a drive recess in a screw head. A press-in cover as claimed in claim I where the *.primary wings have a greater radial dimension than the secondary wings.

3. A press-in cover for an inwardly tapering crucifix shape drive recess in a screw head, where the drive recess has a centre zone with a central axis from which radiates four drive slots each with two sides and an end, the drive slots are equally angularly spaced .around the said central axis and between adjacent drive slots there is a pair of inwardly convergent bearing surfaces: said cover is made of a resiliently deformable material and comprises a head, an elongated substratum integral with the head and having a central ST longitudinal axis which lies normal to an underface of the head, said substratum includes a body which tapers and is largest adjacent said head and includes four drive slot engaging primary wings extending the length of the body and equally angularly spaced around said substratum axis, each wing has an outer face with a longitudinally extending valley in the outer face between two wing edges, said valleys allowing the distance between the wing edges to be decreased by forced wedging engagement of the wing edges with the sides of the drive slots of r. crucifix drive recess, a secondary wing between adjacent primary wings and extending in the length direction, of the body and spaced from the adjacent primary wings by slots, each S.secondary wing has an outer face with a longitudinally .i extending valley in the outer face between two wing edges, the valleys of the secondary wings allowing the distance between the wing edges of the secondary wings to be increased by forced wedging engagement of the secondary wing edges against inwardly convergent bearing surfaces in a crucifix drive recess. re A press-in cover as claimed in claim 3 wherein the valleys in the outer faces of the primary wings and the secondary wings are of Vee cross-sectional shape. A press-in cover as claimed in claim 3 or claim 4- in which the substratum body has a terminal end and said secondary wings terminate short of said terminal 4' end and said primary wings have portions extendiilg beyond said secondary wings and said portions each has a chamfered end face which lies at an angle to said substratum axis where the angle is substantially greater than the angle of taper of said body thereby to form angled leading ends for said primary wings.

6. A press-in cover as claimed in any one of claims 3 to 5 where said body includes a central core portion from which said wings extend and said core portion has a central hole therein which is open to the end of the body remote from said head.

7. A press-in cover as claimed in any one of claims 3 to 6 wherein said head has an undersurface which is a dished with a peripheral under edge which lies in a plane spaced from and above said head underface. 2. A press-in cover for an inwardly tapering crucifix shape drive tool aperture in a screw head as hereinbefore described with reference to the drawings. Dated this 25th day of April, 1993 Dated this 25th day of April, 1993 ABSTRACT A press-in cover for forced insertion into a drive recess in a screw head where it is resiliently retained, where said cover is made of a resiliently deformable material and comprises a head an elongated substratum integral with the head and extending from the underface of the head the substratum is tapered and is largest adjacent the head and includes a plurality of radially extending equally angularly spaced apart wings each wing *OS@ (8,8a) has an outer face with a longitudinally extending valley in the outer face between wing edges, the valleys in the outer faces of the wings (8,8a) o 0 0 allow resilient deflection of the wing edges when the substratum is forceably inserted in a drive recess in a 999 screw head. 0 @94 9 @9 0 @0