GB1564221A - Wall plug - Google Patents

Description

(54) WALL PLUG (71) We, THE UNIVERSAL WALL PLUG COMPANY LIMITED, a British Company of P.O. Box 7, Lichfield, Staffordshire, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to plastics wall plugs for use in securing a screw in a bore in a wall or the like.

The object of the invention is to provide an improved moulded plastics wall plug which is particularly effective in providing a firm anchorage in use, and in which true axial insertion and driving home of the screw is facilitated.

According to the invention there is provided a wall plug formed as a substantially cylindrical moulding of plastics material with a major part of its length extending from one end divided by longitudinal radial slots into at least three gripping legs whose cross sections are sectors of the diametral section of said part of the plug; and the remaining minor part of the plug forming a head portion having a central opening which tapers axially inwardly towards said slots for entry of a screw in three stages, that is a first stage greater in overall diameter than the size of screws to be used with the plug, a second stage having a much less acute taper than the first stage and into the walls of which the screw threads will bite on insertion, and an innermost stage sharply tapered to lead between the three gripping lets.

A preferred embodiment of the invention is now more particularly described with reference to the accompanying drawings wherein; Figure I is a perspective view of a wall plug; Figure 2 is a longitudinal axial section of the plug; Figure 3 is an end view of a head of the plug; Figure 4 is a plan view of a group of plugs as supplied for use; and Figure 5 is an end view of said group.

Referring firstly to Figures 1 - 3 the wall plug 10 is 6 mm nominal diameter, 32 mm long, and is designed for use with screw sizes 4 to 12.

Apart from a small radial flange 11 at the end of a head portion 12, plug 10 is generally cylindrical although it is given a very slight (1/2 ) taper from its maximum diameter adjacent the flange 11.

A 23mm major portion 13 of the total length (i.e. substantially 70%) extending from the end remote from flange 11 up to head portion 12 is divided into three gripping legs 14 by radial slots 15 at 120C angles.

The remaining minor portion 9 mm in length constituting head portion 12 is not slotted but is provided with a shaped central aperture 16 which tapers in three stages 16a, b and c as shown in Figures 2 and 3 so that its axially inner end joins with the narrow central through-aperture formed at the junction of the three slots 15 between legs 14.

The first 3 mm stage 16a of said shaped aperture is greater in overall diameter than the screws used. thus avoiding any distortion or expansion of the flanged end of the plug in use. Stage 16b from 3 mm to 7.5 mm in axial depth has a much less acute taper and the plug wall in this stage is internally shaped to form three equally spaced deepened grooves 17 so that the threads of the screw only bite into areas of the wall surface between these grooves during initial insertion. The shaping of this stage of the tapered aperture is designed to ensure that at least two threads of the screw bite into the walls of the plastics plug simultaneously with a self-tapping action so that the screw is accurately centred and started true on the plug axis.

The innermost stage 16c of aperture 16 from 7.5 mm to 9 mm depth is sharply tapered to lead into the narrow throughaperture, so guiding the screw point centrally between the three legs 14 to ensure that the latter are all spread apart evenly as referred to hereafter. The use of three gripping legs 14 helps to ensure that the screw is maintained on its central path as it is driven along major portion 13 of the plug.

Apart from three small tapered fins 18 extending from flange 11 along head portion 12 only, the plug outer periphery is left as a plain substantially cylindrical surface without fins, ridges or high points so as to maximise the surface area available for gripping pressure within the bore with which the plug is operatively engaged.

The grippings legs 14 in the construction illustrated in the drawings occupy 70% of the total plug length to give maximum effective gripping pressure in the bore. With plug 10 in a free condition (not in a bore) entry of a screw between three legs 14 would displace them angularly by about 30 relative to the plug axis by their flexure at their junction with head portion 12 causing the free end of each leg to be displaced approximately 11 mm radially outwards from its original position. By comparison if legs 14 were only 16 mm long a 30 displacement would only cause outward movement of the free ends by some 7.5 mm.

This increased angular displacement is equivalent to greatly enhanced gripping performance deep within a bore when the plug is in use.

On the other hand, if radially outward flexure of legs takes place too near the outer end of this type of plug, i.e. the legs are more than about 70cue of the total plug length, expansion will occur too near the wall surface and may cause damage to the latter. For this reason the proportions shown in the drawings and described above are preferred.

It is also desirable that the point of maximum grip of a wall plug in the bore is as deep as possible as an axial pull on the screw will tend to displace a volume of most wall materials which is enclosed by a conical envelope extending at 45" to the plug axis outwards from the point of maximum grip.

It will be apparent that the deeper in the wall said point is, the greater will be the volume of wall material tending to be displaced, i.e. the holding quality of the fastening will be greatly enhanced.

Figures 4 and 5 illustrate the manner in which a plurality of plugs 10 is moulded and supplied to the user. flange 11 of each plug being linked to a flat central strip 20 (which can bear details of screw and drill sizes.

brand name etc.) by a pair of connectors 21 each of which is tapered towards flange 11 to facilitate separation of the individual plugs.

WHAT WE CLAIM IS: 1. A wall plug formed as a substantially cylindrical moulding of plastics material with a major part of its length extending from one end divided by longitudinal radial slots into at least three gripping legs whose cross sections are sectors of the diametral section of said part of the plug; and the remaining minor part of the plug forming a head portion having a central opening which tapers axially inwardly towards said slots for entry of a screw in three stages, that is a first stage greater in overall diameter than the size of screws to be used with the plug, a second stage having a much less acute tapet than the first stage and into the walls of which the screw threads will bite on insertion, and an innermost stage sharply tapered to lead between the three gripping legs.

2. A plug acccording to claim 1 wherein said major part is substantially 70% of the total length of the plug.

3. A plug according to claim 1 or 2 having three gripping legs defined by radial slots at 1200 angles.

4. A plug according to claim 1, 2 or 3 wherein the plug is slightly tapered to a minimum diameter at one end.

5. A plug according to claim 4, said taper being substantially l/2 .

6. A plug according to any one of the preceding claims wherein the plug interior wall in the second stage of said tapering is provided with a plurality of deepened grooves so that the screw threads engage only areas of the wall between said groves.

7. A plug according to any one of the preceding claims wherein the head portion has a radial flange surrounding the central opening.

8. A plug according to claim 7 including a plurality of tapered fins extending from said flange along the head portion only, the remainder of the plug periphery being a plain substantially cylindrical surface.

9. A plurality of plugs according to any one of the preceding claims formed as a single moulding, each plug being linked to a flat strip by a pair of tapered connections.

10. A wall plug substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. The innermost stage 16c of aperture 16 from 7.5 mm to 9 mm depth is sharply tapered to lead into the narrow throughaperture, so guiding the screw point centrally between the three legs 14 to ensure that the latter are all spread apart evenly as referred to hereafter. The use of three gripping legs 14 helps to ensure that the screw is maintained on its central path as it is driven along major portion 13 of the plug. Apart from three small tapered fins 18 extending from flange 11 along head portion 12 only, the plug outer periphery is left as a plain substantially cylindrical surface without fins, ridges or high points so as to maximise the surface area available for gripping pressure within the bore with which the plug is operatively engaged. The grippings legs 14 in the construction illustrated in the drawings occupy 70% of the total plug length to give maximum effective gripping pressure in the bore. With plug 10 in a free condition (not in a bore) entry of a screw between three legs 14 would displace them angularly by about 30 relative to the plug axis by their flexure at their junction with head portion 12 causing the free end of each leg to be displaced approximately 11 mm radially outwards from its original position. By comparison if legs 14 were only 16 mm long a 30 displacement would only cause outward movement of the free ends by some 7.5 mm. This increased angular displacement is equivalent to greatly enhanced gripping performance deep within a bore when the plug is in use. On the other hand, if radially outward flexure of legs takes place too near the outer end of this type of plug, i.e. the legs are more than about 70cue of the total plug length, expansion will occur too near the wall surface and may cause damage to the latter. For this reason the proportions shown in the drawings and described above are preferred. It is also desirable that the point of maximum grip of a wall plug in the bore is as deep as possible as an axial pull on the screw will tend to displace a volume of most wall materials which is enclosed by a conical envelope extending at 45" to the plug axis outwards from the point of maximum grip. It will be apparent that the deeper in the wall said point is, the greater will be the volume of wall material tending to be displaced, i.e. the holding quality of the fastening will be greatly enhanced. Figures 4 and 5 illustrate the manner in which a plurality of plugs 10 is moulded and supplied to the user. flange 11 of each plug being linked to a flat central strip 20 (which can bear details of screw and drill sizes. brand name etc.) by a pair of connectors 21 each of which is tapered towards flange 11 to facilitate separation of the individual plugs. WHAT WE CLAIM IS:

1. A wall plug formed as a substantially cylindrical moulding of plastics material with a major part of its length extending from one end divided by longitudinal radial slots into at least three gripping legs whose cross sections are sectors of the diametral section of said part of the plug; and the remaining minor part of the plug forming a head portion having a central opening which tapers axially inwardly towards said slots for entry of a screw in three stages, that is a first stage greater in overall diameter than the size of screws to be used with the plug, a second stage having a much less acute tapet than the first stage and into the walls of which the screw threads will bite on insertion, and an innermost stage sharply tapered to lead between the three gripping legs.

2. A plug acccording to claim 1 wherein said major part is substantially 70% of the total length of the plug.

3. A plug according to claim 1 or 2 having three gripping legs defined by radial slots at 1200 angles.

4. A plug according to claim 1, 2 or 3 wherein the plug is slightly tapered to a minimum diameter at one end.

5. A plug according to claim 4, said taper being substantially l/2 .

6. A plug according to any one of the preceding claims wherein the plug interior wall in the second stage of said tapering is provided with a plurality of deepened grooves so that the screw threads engage only areas of the wall between said groves.

7. A plug according to any one of the preceding claims wherein the head portion has a radial flange surrounding the central opening.

8. A plug according to claim 7 including a plurality of tapered fins extending from said flange along the head portion only, the remainder of the plug periphery being a plain substantially cylindrical surface.

9. A plurality of plugs according to any one of the preceding claims formed as a single moulding, each plug being linked to a flat strip by a pair of tapered connections.

10. A wall plug substantially as hereinbefore described with reference to and as shown in the accompanying drawings.