GB2445750A

GB2445750A - System for mounting cladding panels to a structure

Info

Publication number: GB2445750A
Application number: GB0701091A
Authority: GB
Inventors: John O'donnell
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-01-20
Filing date: 2007-01-20
Publication date: 2008-07-23
Also published as: US20100115871A1; GB0701091D0; GB2457863A; WO2008087406A1; GB0912458D0

Abstract

The invention relates to a mounting member for mounting cladding panels such as plasterboard panels to walls or ceilings. The mounting member comprises a body 2 in which a first aperture 24 is located in a first wall 4 of the body, and a second aperture 26, is located in a second wall 6 of the body. The apertures are co-axial with the second aperture preferably countersunk to receive the head of a fixture (601 figure 6). The mounting member also comprises at least one pair of flanges 12 projecting from a third wall 8 of the body, the flanges defining an inwardly tapering channel 16 adapted to receive a portion of the cladding panels. The mounting member may be manufactured from extruded plastics in long lengths and cut to size. Also included is a fixture (601 figure 6) for securing the mounting members to the structure.

Description

244575Q

SYSTEM FOR MOUNTING CLADDING PANELS TO A STRUCTURE

The present invention is directed to a system and method for mounting cladding panels, particularly to walls and ceilings. The system is especially suited to, although not limited to, use in the mounting of plasterboard panels in buildings.

At present, when interior cladding panels such as plasterboard are to be mounted to the walls and ceilings of a building, the process requires a great deal of manual effort from joiners or fitters. Usually, the mounting of such panels is a job carneci out by two person teams. Dunng the mounting process, the two individuals must balance the panels while at the same time attach the panels to structural elements such as joists or stud partitions. The attachment is normally achieved by fixtures such as nails or screws being pushed through the panel into the structural element by a nail gun or the like. In order to balance the panel whilst applying the fixtures, the fitters are often using their head or shoulder to support the panel, particularly when fitting ceiling panels. Such practices can greatly increase fatigue in the fitters and also cause injury.

Once the panels are mounted, conventional practice requires that the join between the panels is covered before a plaster coating is applied over the panels and the join. The join is normally covered using a suitable tape.

Having to tape over the join in this way increases the time taken to prepare the panelled area for plastering.

Ills an aim of the present invention to obviate or mitigate one or both of the aforementioned disadvantages.

According to a first aspect of the present invention, there is provided a mounting member for mounting a cladding panel to a structure, the mounting member comprising: a body: a first aperture located in a first wall of the body, and a second aperture located in a second wall of the body, wherein the apertures are substantially co-axial and adapted to receive a fixture therein; and at least one pair of flanges projecting for a third wall of the body, the pair of flanges defining a channel adapted to receive a portion of a cladding panel.

Preferably, the pair of flanges are adapted such that the channel has a greater width at the third wall than at the end of the flanges remote from the body.

Preferably, the mounting member further comprises a second pair of flanges projecting from a fourth wall of the body, the second pair of flanges defining a second channel adapted to receive a portion of a further cladding panel.

Preferably, the first and second pairs of flanges are adapted such that the first and second channels have a greater width at the third and fourth walls, respectively, than at the end of the flanges remote from the body.

In one preferred embodiment, the third and fourth walls of the body are substantially parallel to one another. Most preferably, the body is cuboidal, and the first, second, third and fourth walls define the walls of the cuboid.

Preferably, the second aperture is a countersunk aperture. In other words, the diameter of the second aperture is greater at the second wall than at any point internal of the body.

In another, alternative, preferred embodiment, the body has a substantially L-shaped profile and the third and fourth walls are substantially at right angles to one another.

Preferably, the second wall comprises first and second portions, wherein the first portion is substantially at right angles to the second portion. Most preferably, the second aperture is located at the vertex of the angle between the first and second portions.

Preferably, the body and flanges are elongate and the mounting member comprises a plurality of pairs of first and second apertures spaced along the length of the body.

Preferably, the mounting member further comprises fifth and sixth walls which are substantially at right angles to the first and second walls, respectively, and a third aperture located in a fifth wall of the body, and a fourth aperture in a sixth wall of the body, wherein the third and fourth apertures are substantially co-axial and adapted to receive a second fixture therein.

Preferably, the second and fourth apertures are countersunk apertures. In other words, the diameter of the second and fourth apertures is greater at their respective walls than at any point internal of the body.

Preferably, the body and flanges are elongate and the mounting member comprises a plurality of pairs of first and second, and third and fourth, apertures spaced along the length of the body.

According to a second aspect of the invention, there is provided a concealing member for concealing a gap between adjacent cladding panels, the concealing member comprising: a body adapted to locate in use in the gap; a first aperture located in a first wall of the body, and a second aperture located in a second wall of the body, wherein the apertures are substantially co-axial and adapted to receive a fixture therein; a first flange projecting for a third wall of the body: and a second flange projecting from a fourth wall of the body; wherein the third and fourth walls of the body are substantially parallel to one another, and in use abut the adjacent ends of the cladding panels.

Preferably, each of the first and second flanges tapers to an edge remote from the body. In other words, the thickness of each flange reduces the further the flange is from the body.

Preferably, the first and second walls are substantially parallel to one another and a portion of each flange adjacent the body is co-planar with the second wall. Preferably, the edge of each flange remote from the body is closer to the plane of the first wall than the portion of each flange adjacent the body. In other words, each flange is curved from the body to the remote edge.

Preferably, the body is cuboidal, and the first, second, third and fourth walls define the walls of the cuboid.

H

Preferably, the second aperture is a countersunk aperture. In other words, the diameter of the second aperture is greater at the second walls than at any point internal of the body.

Preferably, the body and flanges are elongate and the concealing member comprises a plurality of pairs of first and second apertures spaced along the length of the body.

According to a third aspect of the invention, there is provided a fixture comprising: an elongate body having a helical thread formed thereon; and a head comprising a first end attached to an end of the body and a second end remote from the body; wherein the first end of the head has a greater diameter than the threaded body such that an abutment is formed between the body and the head, and the second end of the head includes a lip portion having a greater diameter than remainder of the head, the external circumference of the lip portion having a rounded profile.

Preferably. the head has a concave profile where its diameter increases from the first end towards the lip portion.

Preferably, the head has an axial length greater than the largest diameter of the lip portion.

According to a fourth aspect of the invention, there is provided a method of mounting a cladding panel to a structure comprising a plurality of structural elements, the method comprising the steps of: fixing one or more first mounting members in accordance with the first aspect of the invention to a structural element; locating a first end of a cladding panel in a channel of the first mounting member whilst supporting a second end of the cladding panel; locating the second end of the cladding panel in a channel of one or more second mounting members; and fixing the second mounting member to an adjacent structural element.

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a mounting member for mounting at least two cladding panels to a structure; Figure 2 is a perspective view of a mounting member for mounting at least one cladding panel to a structure; Figure 3 is a perspective view of a mounting member for mounting at least two cladding panels to an external corner of a structure; Figure 4 is a perspective view of a mounting member for mounting at least two cladding panels to an internal corner of a structure; Figure 5 is a perspective view of a member for concealing the join between adjacent cladding panels; and Figure 6 is a fixture for securing cladding panels to a structure.

Figure 1 shows a mounting member, generafly designated 1, for mounting cladding panels to a structure. The mounting member 1 comprises a body 2 which is preferably cuboidal and hollow. The shape of the body 2 is defined by an upper wall 4, a lower wall 6 and a pair of side walls 8,10.

Extending outwardly from the respective side walls 8,10 are a pair of flanges 12,14. Along with their respective side walls 8,10, the pairs of flanges 12,14 define a pair of channels 16,18 extending along opposite sides of the body 2. Each flange 12,14 of a pair is formed such that they taper to an edge 20,22 remote from the body 2. In addition, each flange is also formed such that it curves inwardly towards the other flange of the pair. As a result, the width WI of the channels 16,18 adjacent the side waIls 8,10 of the body 2 is greater than the width W2 of the channels 16,18 at the edges 20,22 of the flanges 12,14 remote from the body 2.

The upper and lower waIls 4,6 of the body contain an inner aperture 24 and a outer aperture 26, respectively. The apertures 24,26 are co-axial in order to receive a fixture as will be explained below. The outer aperture 26 has an internal opening 28 and is countersunk, wherein the diameter of its external opening 27 is greater than that of any other portion of the aperture 26. This allows the head of a fixture put through the body 2 to lie within the outer aperture 26 instead of protruding therefrom.

The body 2 and the pairs of flanges 12.14 are preferably integrally formed from a resilient plastics material. The plastics material is preferably extruded into the required form and can be extruded in short sections, as shown here in Figure 1, or else in extended lengths of around 5-6m. In the case of the extended lengths, these can be cut to a preferred length after extrusion. In one preferred embodiment, the lengths are cut into 2.4m long sections. In order for the members 1 to be fixed to regularly spaced structural elements, such as floor joists or the studs of a stud partition wall, the co-axial apertures 24,26 are spaced along the extended lengths such that their centres are 60cm apart. This spacing is dictated by the requirements of building regulations, which require the structural elements of floors, ceilings and the like to be themselves 60cm apart.

Figure 2 shows an alternative embodiment of the mounting member shown in Figure 1. In Figure 2, the mounting member 101 is identical to the mounting member of Figure 1, save for the fact that only one pair of flanges 112 is provided on the side wall 108 of the body 102. With the side wall 108, the pair of flanges 112 define a channel 116 extending along one side of the body 102. The upper and lower walls 104,106 of the body 102 contain an inner aperture 124 and a outer aperture 126, respectively. The apertures 124,126 are co-axial in order to receive a fixture as will be explained below. As with the embodiment of Figure 1, the outer aperture 126 has an internal opening 128 and is countersunk.

The way in which the mounting members are used will now be described.

Initially, individual mounting members or lengths thereof are fixed to the structural elements (e.g. joists, beams or studs) of the structure being clad.

These mounting members are intended to hold a first end of a cladding panel. The mounting members are held against the structural elements so that the upper wall 4,104 of the body 2,102 lies along the structural element, with the lower wall 6,106 facing away from the structural element.

Fixtures are then applied through the apertures 24,26,124,126 into the structural elements to fix the members 1,101 to the structural elements.

As will become apparent, the embodiments of the mounting members shown in Figures 1 and 2 are for different applications. The first embodiment of Figure 1 is intended for use in the midst of a ceiling or wall, for example, when cladding panels are to be mounted on either side of the structural element to which the mounting member is fixed. In contrast, the second embodiment of the mounting member, as shown in Figure 2, is intended for use where a cladding panel is only required on one side of a structural element. An example of such an instance would be where the structural element is the first or last joist in a ceiling where the ceiling meets a structural wall.

Once the first mounting members have been fixed to a structural element, a first end of a cladding panel, such as a plasterboard panel for example, is slid into the channel 16,116 of the fixed mounting member. The inward taper of the flanges 12,112 defining the channel ensure a frictional engagement with the first end of the panel, as the panel thickness is greater than the width W2 of the channel, but less than the width Wi of the channel. Once the first end of the panel is supported by the first mounting member(s), a fitter supports the second end of the panel while they engage the second end of the panel with the channel 18 of at least one second mounting member. Again, the taper of the flanges 14 forming the channel ensures a frictional engagement with the second end of the panel. Once the second mounting member has engaged the second end of the panel, the fitter lifts the second end of the panel and mounting member(s) until the upper wall 4 contacts an adjacent structural element.

More fixtures are then applied through the apertures 24,26 of the second mounting member into the structural element to fix the second mounting member thereto. The cladding panel is then held against the structural elements by the first and second mounting members. If a number of panels are required to clad a wall or ceiling, for example, the process can be repeated using additional mounting members of the type shown in Figure 1. For the final structural element, a mounting member of the type shown in Figure 2 will be used to complete the process.

The embodiments of the mounting member shown in Figures 1 and 2 are for use in situations where a continuous, substantially flat surface is to be clad. However, there are instances where the surface being clad will include both external and internal corners. The embodiments of Figures 3 and 4 are for use in this instance.

Figure 3 shows a mounting member, generally designated 301, for mounting cladding panels around an external corner. The mounting member 301 comprises a body 302 which itself comprises first and second body portions 303,305. The first and second body portions 303,305 lie substantially at right angles to one another. The first body portion 303 has a first side wall 308 remote from the second body portion 305, whilst the second body portion 305 has a second side wall 310 remote from the first body portion 303. The body 301 has a substantially L-shaped profile such that the first and second side walls 308,310 are substantially at right angles to one another. Extending outwardly from the respective side walls 308,310 are a pair of flanges 312,314. Along with their respective side walls 308,310, the pairs of flanges 312,314 define a pair of channels 316,318 extending substantially at right angles to one another along opposite sides of the body 302. Each flange 312,314 of a pair is formed in the same manner as those in the embodiments of Figures 1 and 2, with the same taper and consequent difference in width of the channel at WI and W2. Each of the first and second body portions has an inner aperture 324 and a outer aperture 326, respectively. The apertures are identical to those of the embodiments of Figures 1 and 2.

As with the previously described embodiments, the body 302 and the pairs of flanges 312,314 are preferably integrally formed from a resilient plastics material. The plastics material is preferably extruded into the required form and can be extruded in short sections, as shown here in Figure 3, or else in extended lengths of around 5-6m. In the case of the extended lengths, these can be cut to a preferred length after extrusion. In one preferred embodiment, the lengths are cut into 2.4m long sections. In order for the members 1 to be fixed to regularly spaced structural elements, such as floor joists or the studs of stud partions, the co-axial apertures 324.326 are spaced along the extended lengths such that their centres are 60cm apart. This spacing is dictated by the requirements of building regulations, which require the structural elements of floors, ceilings and the like to be themselves 60cm apart.

Figure 4 shows a further embodiment of a mounting member, generally designated 401, for mounting cladding panels in an internal corner. The mounting member 401 is similar to the embodiment shown in Figure 3. In the interests of brevity, the features of the embodiment of Figure 4 which are identical to those of the embodiment of Figure 3 will not be described again here. Instead, each feature which is identical has simply been assigned a replacement reference number in Figure 4 which is prefixed with "4_" instead of "3_". Where the fourth embodiment differs from the third embodiment is in the location of the apertures for receiving a fixture.

The inner aperture (not shown) and outer aperture 426 are arranged co-axially in the body 402 such that their shared axis passes through the vertex of the substantially 90 angle between the first and second body portions 403,405. As a result, a fixture inserted through the inner and outer apertures will enter directly into the internal corner of the structural element.

The third and fourth embodiments of the mounting member can be utilised in substantially the same manner as the first and second embodiments. In other words, the channels 312,314,412,414 are adapted to receive an end of a cladding panel, either before or after the mounting members 301,401 have been fixed to a structural element.

The first to fourth embodiments of the mounting members are adapted such that the body portions of the members will cover the gaps between the ends of adjoining cladding panels which are held in the channels of the mounting members. However, gaps between the ends of the panels which are transverse to the mounting members, and hence not held by the mounting members, will still be visible. These gaps are covered by the concealing member illustrated in Figure 5.

The concealing member, generally designated 501, comprises a body 502 which is preferably cuboidal and hollow. The shape of the body 502 is defined by an upper wall 504, a lower wall 506 and a pair of side walls 508,510. Extending outwardly from the respective side walls 508,510 are a pair of flanges 512. The body 502 and the pair of flanges 512 give the concealing member 501 a shape in the form of an inverted "1". Each flange 512 is formed such that it tapers to an edge 520 remote from the body 502. In addition, each flange 512 is also formed such that it curves upwardly (when viewed in Figure 5) towards the body 502.

The upper and lower waIls 504,506 of the body 502 contain an inner aperture 524 and an outer aperture 526, respectively. The apertures 524,526 are co-axial in order to receive a fixture as will be explained below. The outer aperture 526 is countersunk, allowing the head of a fixture put through the body 502 to lie within the outer aperture 526 instead of protruding therefrom.

The body 502 and flanges 512 are preferably integrally formed from a resilient plastics material. The plastics material is preferably extruded into the required form and can be extruded in short sections, as shown here in Figure 5, or else in extended lengths of around 5-6m. In the case of the extended lengths, these can be cut to a preferred length after extrusion.

In one preferred embodiment, the lengths are cut into 2Am long sections.

In order for the members 1 to be fixed to regularly spaced structural elements, such as floor joists or the studs of stud partions, the co-axial apertures 524,526 are spaced along the extended lengths such that their centres are 60cm apart.

In use, the concealing member 501 is applied in much the same way as the mounting members. The lengths of the concealing member 501 are positioned so that the body 502 locates in the transverse gap between adjoining cladding panels with the upper side (when viewed in Figure 5) of the flanges 512 contacting the cladding panels. The concealing member 501 is then fixed to an appropriate structural element by a fixture applied through the apertures 524, 526. If desired, further fixtures can be applied directly through the flanges 512 and cladding panels into the structural element. With the concealing members in place, a smooth surface is presented for plastering or similar surface treatment.

A fixture suitable for fixing the mounting and concealing members to structural elements in shown in Figure 6. The fixture, generally designated 601, comprises an elongate body 602 and a head 604 located at a first end 605 of the body 602. The body 602 has a second end 608 remote from the head 604 which tapers to a point 610. The body also includes a helical thread 606 running the length thereof, the thread ending adjacent the point 610. The head 604 has a first end 612 adjacent the first end 605 of the body 602 and a second end 614 remote from the body 602. The first end 612 of the head 604 has a larger diameter than that of the body 602 and the thread 606 combined. As a result, a step or abutment 616 is formed between the first end 605 of the body 602 and the first end 612 of the head 604. The surface of the step 616 faces towards the second end 608 of the body 602. The head 604 also has an intermediate portion 613 between its first and second ends 612,614. The diameter of the head 604 increases from the first end 612 through the intermediate portion 613 to a lip portion 618 at the secdnd end 614. Consequently, the head 604 has a concave profile when the fixture is viewed from the side in the manner seen in Figure 6. The lip 618 has a diameter that is greater than any diameter of the remainder of the head 604. The lip 618 has an outer circumference which has a rounded profile, where the two portions of the lip 618 closest and farthest away from the body 602 have diameters which are smaller than the diameter of a portion of the lip lying between those closest and farthest away portions. The head has an axial length L greater than the largest diameter D of the lip portion 618.

In use, the fixture 601 will be driven into a structural element (usually made of wood) directly or else through a cladding panel first. The second end of the head 604 includes one or more grooves (not shown) for receiving the head of an appropriate driving tool. As the fixture 601 is driven, it will rotate and the thread 606 will grip into the receiving material.

During this process, loose material will pass back along the thread 606 in the direction of the head 604. The step 616 provided on the head 604 ensures that none of the loose material can pass by the head 604 during the driving process. Instead, the loose material is compacted by the step 616 as the fixture is driven further into the substrate. This is particularly beneficial if the fixture is being initially driven through a relatively friable material such as plasterboard, as the compacted material improves the hold between the fixture and the plasterboard.

Once the fixture 601 is driven into the structural element, the step 616 plays a further role in ensuring that the fixture is not driven in too far.

Thus, the fixture cannot be driven further into a surface once the entire thread is in the surface due to the step 616 preventing any further movement in the direction of driving. Additionally, by ensuring that the transition area 620 between the intermediate portion 613 and the lip 618 has a radius of curvature and is non-planar, no flat surfaces are presented which could damage the surface as the fixture 601 is being driven.

Instead, the curved transition area 620 and rounded profile of the lip 618 compress the surrounding material in the surface in a number of directions, thereby avoiding any large shear forces on adjacent material in the surface.

The mounting members of the present invention ensure that cladding panels can be mounted to structural elements without the panels being fixed directly to the elements by fixtures. As a result, the risk of breaking cladding panels, especially where they are made from plasterboard, is greatly reduced. A fitter does not have to be concerned with how far from an edge of the panel they can use a fixture without cracking or breaking the panel.

Additionally, the mounting members make it easier for pairs of fitters or joiners to clad a structure. By being able to engage one end of the panel in mounting members already fitted to a structural element, a fitter does not need to support the panel or apply fixtures directly to the panel itself.

Consequently, fitters can avoid the injuries and discomfort that can occur when having to support and fit a panel at the same time.

Both the mounting and concealing members offer a further benefit in that they conceal the gaps between adjacent cladding panels. This removes the need for any additional concealing steps such as the application of a concealing tape over the gaps. A plaster coating can therefore be applied over the members and cladding panels immediately. By ensuring that the outer, and thus exposed, apertures of each member are countersunk, the heads of the fixtures used are concealed below the exposed surface of the members.

The fixture of the present invention, as shown in Figure 6, offers additional benefits for the fitter. As described above, the step between the threaded body and the head of the fixture ensures that material loosened during the driving process is compacted. Consequently, the fixture has an improved grip in the surrounding material. The step also ensures that the fixture cannot be driven too far into the surface. By ensuring that the transition area between the intermediate portion of the fixture head and the lip has a radius of curvature and the lip has a rounded profile, the risk of breaking relatively friable materials such as plasterboard is reduced. Most conventional fixtures comprise a planar surface between the body of the fixture and the lip, where the surface either faces directly towards the material surface or is at an angle thereto. In either case, the flat surface means that large shear forces are applied to the surface material as the fixture is driven in. This often causes fracturing of the surface material. In ensuring that all surfaces of the head of the fixture are non-planar, such fracturing is avoiding with the fixture of the present invention.

The bodies of the members are preferably hollow and guide blocks can be provided to ensure that abutting lengths of the members are correctly aligned. Opposite ends of a guide block are fixed into the abutting open ends of the bodies when they are fixed to the structural elements.

These and other modifications and improvements can be incorporated without departing from the scope of the invention.

Claims

CLAIMS: 1. A mounting member for mounting a cladding panel to a

structure, the mounting member comprising: a body; a first aperture located in a first wall of the body, and a second aperture located in a second wall of the body, wherein the apertures are substantially co-axial and adapted to receive a fixture therein; and at least one pair of flanges projecting for a third wall of the body, the pair of flanges defining a channel adapted to receive a portion of a cladding panel.
2. The mounting member of Claim 1, wherein the pair of flanges are adapted such that the channel has a greater width at the third wall than at the end of the flanges remote from the body.
3. The mounting member of Claim 1 further comprising a second pair of flanges projecting from a fourth wall of the body, the second pair of flanges defining a second channel adapted to receive a portion of a further cladding panel.
4. The mounting member of Claim 3, wherein the first and second pairs of flanges are adapted such that the first and second channels have a greater width at the third and fourth walls, respectively, than at the end of the flanges remote from the body.
5. The mounting member of either Claim 3 or Claim 4, wherein the third and fourth walls of the body are substantially parallel to one another.
6. The mounting member of Claim 5, wherein the body is cuboidal, and the first, second, third and fourth walls define the walls of the cuboid.
7. The mounting member of any preceding claim, wherein the diameter of the second aperture is greater at the second wall than at any point internal of the body.
8. The mounting member of either Claim 3 or Claim 4, wherein the body has a substantially L-shaped profile and the third and fourth walls are substantially at right angles to one another.
9. The mounting member of Claim 8, wherein the second wall comprises first and second portions, wherein the first portion is substantially at right angles to the second portion.
10. The mounting member of Claim 9, wherein the second aperture is located at the vertex of the angle between the first and second portions of the second wall.
11. The mounting member of any preceding claim, wherein the body and flanges are elongate and the mounting member comprises a plurality of pairs of first and second apertures spaced along the length of the body.
12. The mounting member of Claim 8 further comprising fifth and sixth walls which are substantially at right angles to the first and second walls, respectively, and a third aperture located in the fifth wall of the body, and a fourth aperture located in the sixth wall of the body, wherein the third and fourth apertures are substantially co-axial and adapted to receive a second fixture therein.
13. The mounting member of Claim 12, wherein the diameter of the second and fourth apertures is greater at their respective walls than at any point internal of the body.
14. The mounting member of either Claim 12 or Claim 13, wherein the body and flanges are elongate and the mounting member comprises a plurality of pairs of first and second, and third and fourth, apertures spaced along the length of the body.
15. A method of mounting a cladding panel to a structure comprising a plurality of structural elements, the method comprising the steps of: fixing one or more first mounting members in accordance with any of Claims I to 14 to a structural element; locating a first end of a cladding panel in a channel of the first mounting member whilst supporting a second end of the cladding panel; locating the second end of the cladding panel in a channel of one or more second mounting members; and fixing the second mounting member to an adjacent structural element.
16. A fixture comprising: an elongate body having a helical thread formed thereon; and a head comprising a first end attached to an end of the body and a second end remote from the body; wherein the first end of the head has a greater diameter than the threaded body such that an abutment is formed between the body and the head, and the second end of the head includes a lip portion having a greater diameter than remainder of the head, the external circumference of the lip portion having a rounded profile.
17. The fixture of Claim 16, wherein the head has a concave profile where its diameter increases from the first end towards the lip portion.
18. The fixture of either Claim 16 or Claim 17, wherein the head has an axial length greater than the largest diameter of the lip portion.