WO2024032868A1

WO2024032868A1 - Disc shaped throwing object comprising an air cushion element and a rim element

Info

Publication number: WO2024032868A1
Application number: PCT/EP2022/072219
Authority: WO
Inventors: Axel VON HELAND
Original assignee: Waboba Ab
Priority date: 2022-08-08
Filing date: 2022-08-08
Publication date: 2024-02-15

Abstract

A disc shaped throwing object (10) comprises a central air cushion element (12) centred around a central axis (AX) and fastened to an encircling rim element (14), wherein the rim element (14) is made of a first material and the central air cushion element (14) comprises a second material, where the first material has a first GSM value and the second material has a second lower GSM value.

Description

DISC SHAPED THROWING OBJECT COMPRISING AN AIR CUSHION ELEMENT AND A RIM ELEMENT

TECHNICAL FIELD

The invention relates to a disc shaped throwing object that comprises an air cushion element and a rim element.

BACKGROUND

Disc shaped throwing objects such as Frisbees™ are popular to use for recreational purposes.

They may also be soft, which may be of advantage if it is desirable that people should not be hurt if being hit by them or if they are to be made foldable.

WO 2020/071973 discloses one such soft and foldable throwing object.

However, it is of interest to make the object lighter while at the same time retaining or even improving on the flight properties.

SUMMARY

The present invention addresses one or more of the above-mentioned problems.

A first aspect of the invention is concerned with a disc-shaped throwing object comprising a central air cushion element centred around a central axis and fastened to an encircling rim element, wherein the rim element is made of a first material and the central air cushion element comprises a second material, where the first material has a first GSM value and the second material has a second lower GSM value.

GSM is an acronym for grams per square meter.

The first GSM value maybe above 600 g/m² and the second GSM value may be below 600 g/m². It is additionally possible that the second GSM value is below 500 g/m². It may as an example be about 420 g/m². It is furthermore possible that the first GSM value is above 8oo g/m². It may as an example be about 890 g/m².

The first material may be a material in a group of non-hard plastic and/ or rubber materials, such as a thermoplastic elastomer (TPE) like thermoplastic polyurethane (TPU), a thermoplastic rubber (TPR), polyurethane (PU), styrene-butadiene rubber (SBR) and polyvinylchloride (PVC).

The hardness of the first material maybe a Shore A hardness of above 85 and below 98. The Shore A hardness may with advantage be a hardness of 95.

The second material may be a cloth, for instance in the form of a web of woven strands of fibre material, such as nylon, cotton or silk fibres. The cloth may have an air permeability 1/ (m²*s) that is above 100 and below 400 1/ (m²*s). It may for instance be an air permeability of 2001/ (m²*s).

The air cushion element may additionally comprise a number of layers, where the second material is one of the layers. Another layer may in this case be a plastic/ and or rubber material layer, for instance of the same type as the first material or of another material, for instance another material in the above- mentioned group of non-hard plastic and/ or rubber materials.

The air cushion element may comprise an air cushion part centred around the central axis and joined to a supported part, while the rim element may comprise a supporting part of annular shape being placed axially adjacent and in abutment with the supported part. The air cushion part may have a first edge that faces inwards towards the central axis and a second edge that is joined to a first edge of the supported part. The supporting part may in turn have a first edge that faces inwards towards the central axis.

The air cushion element may comprise a first fastening part joined to the supported part. It is in this case also possible that a first edge of the first fastening part is joined to a second edge of the supported part. Thereby the first fastening part may be joined to the air cushion part via the supported part. The rim element may in turn comprise a second fastening part joined to the supporting part. It is in this case possible that a first edge of the second fastening part is joined to a second edge of the supporting part.

The first fastening part may be fastened to the second fastening part. The first fastening part may be fastened to the second fastening part via sewing, stitching, gluing or heat pressing.

The rim element may additionally comprise a concealing part that is joined to the second fastening part. Thereby the concealing part may be joined to the supporting part via the second fastening part. It is in this case furthermore possible that the concealing part has a first edge joined to a second edge of the second fastening part.

The concealing part may additionally be folded over the second fastening part so that the first fastening part is fastened to the second fastening part in a cavity of the rim element formed between the second fastening part and the concealing part when the concealing part is folded over the second fastening part.

When the air cushion element is fastened to the rim element, an inner volume of the throwing object may be defined by the air cushion part, the supporting part and the second fastening part. The air cushion part, the supporting part and the second fastening part each has an inner surface facing this inner volume and an outer surface facing away from the inner volume. Also the concealing part has an inner and an outer surface, where the inner surface is the surface that faces the inner volume after folding has been performed and the outer surface is the surface that faces away from the inner volume after folding has been performed.

Moreover, the outer surface of the concealing part may be aligned with the outer surface of the supporting part when the concealing part has been folded over the second fastening part. The supporting part and the second fastening part may together have an essentially L-shaped cross-section, while the concealing part may have an essentially C- or boomerang shaped cross-section.

After folding, one end of the C or boomerang that forms the first edge of the concealing part may be joined with the second edge of the second fastening part and another end of the C or boomerang that forms the second edge of the concealing part may abut the air cushion element at the point where the supporting part joins the second fastening part.

The throwing object may have a first radius, which first radius may be an outer radius of the supporting part. The first radius may be in the range 70 - 90 mm and with advantage be 83.2 mm. The air cushion part of the air cushion element 12 may have a second radius, which may also be the inner radius of the supporting part. The second radius may be in the range of 40 - 85 and with advantage be 52 mm.

The first radius may with advantage be in the range of 2.25 - 1.05 times larger than the second radius and with advantage 1.6 times larger than the second radius.

The air cushion element may have a first thickness in the range of 1.5 - 2.1 mm and the first thickness may with advantage be 1.8 mm, which first thickness Ti maybe the same throughout the whole air cushion element.

The throwing object also has a height that maybe in the range 14 - 16 mm and may with advantage be 14.8 mm.

The height may additionally be in the range 6.6 - 10.7 higher than the first thickness and with advantage 8.2 times higher than the first thickness.

The rim element may in turn have a thickness that varies. Starting from the first edge of the supporting part that is radially closest to the axis and continuing to the second edge of the concealing part via the second fastening part, the thickness variation maybe the following: The first edge of the supporting part that is closest to the central axis may have a second thickness at the second radius. Thereafter the thickness increases in the direction towards the second fastening part and at the point where the second edge of the supporting part is joined to the first edge of the second fastening part the rim element may have a third thickness, which may be the maximum thickness of the whole rim element. Thereafter, in the second fastening part, the thickness may decrease to a fourth thickness at the point where the second edge of the second fastening part is joined to the first edge of the concealing part, which fourth thickness may be the lowest thickness of the rim element. The thickness may then increase to a fifth thickness, which may be the maximum thickness of the concealing part and thereafter decrease to a sixth thickness, which may be the thickness at the second edge of the concealing part.

The second thickness may for instance be 2.8 mm, the third thickness may for instance be 5.3 mm, the fourth thickness may for instance be 0.6 mm and the sixth thickness may for instance be 1.23 mm. The fifth thickness may range between 5.0 and 13.5 mm and may with advantage be 5.3 mm.

The third thickness at the point where the second edge of the supporting part is joined to the first edge of the second fastening part may be in the range 2 - 4 times larger than the first thickness and with advantage 2.9 times larger than the first thickness.

A second aspect of the invention may be concerned with a method of assembling a throwing object according to the first aspect comprising an air cushion element with an air cushion part centred around a central axis, a supported part and a first fastening part and a rim element with a supporting part and a second fastening part, which second fastening part is angled away from the supporting part with an angle.

The method may compromise the following steps: placing the air cushion element onto the rim element so that the supported part is located axially above the supporting part. placing the first fastening part over the second fastening part so that the first and second fastening parts are aligned with each other, and fastening the first fastening part to the second fastening part,

The rim element may additionally comprise a concealing part that is joined to the second fastening part.

In this case the method may additionally comprise folding, after the first and second fastening parts have been fastened to each other, the concealing part over the second fastening part.

The concealing part may additionally be folded over the second fastening part around a point where the second fastening part is joined to the concealing part.

Through the placing of the air cushion element onto the rim element so that the supported part is located axially above the supporting part, the supporting part is located axially underneath the supported part in the axial direction. Thus, the supporting part is also being placed axially adjacent and in abutment with the supported part. Thereby, the supported part is aligned with and supported by the supporting part, while the air cushion part is unsupported.

Through the placing of the first fastening part over the second fastening part the first fastening part is also located radially outside the air cushion part and the supported part. It is also angled away from the supported part with the same angle with which the second fastening part is angled away from the fastening part.

The fastening of the first fastening part to the second fastening part may be made through sewing, stitching, gluing or heat pressing.

The invention has a number of advantages. The rim element made of the first material may improve the stability of the throwing object in air. The use of the second material has the advantage of lowering the weight and thereby the throwing object can glide in the air longer than if the throwing object was solely made up of the first material.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described, by way of example, with reference being made to the accompanying drawings, in which:

Fig i shows a perspective view of a disc-shaped throwing object with an air cushion element being fastened to a rim element,

Fig. 2 shows a perspective view of the air cushion element and the rim element before having been assembled into the disc-shaped throwing object, Fig. 3 shows a cross-sectional view of the disc-shaped throwing object when the air cushion element is fastened to the rim element, and

Fig. 4 shows a cross-sectional view of the disc shaped throwing object before assembly of the throwing object has been completed.

DETAILED DESCRIPTION

The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description. Fig i schematically shows a perspective view of a disc-shaped throwing object io with an air cushion element 12 being fastened to a rim element 14, fig. 2 schematically shows a perspective view of the air cushion element 12 and the rim element 14 before having been assembled into the disc-shaped throwing object, fig. 3 shows across-sectional view of the disc-shaped throwing object when the air cushion element 12 is fastened to the rim element 14 and fig. 4 shows a cross-sectional view of the disc shaped throwing object before assembly has been completed . Fig. 2 and 4 thereby show the disc-shaped throwing before assembly and fig. 1 and 3 after assembly.

As can be seen in the above-mentioned figures the throwing object 10 is disc shaped. Moreover, the object 10 comprises a central air cushion element 12 that is centred around a central axis AX. The element 12 is termed an air cushion element, because in use it is supposed to be lifted by an air cushion. The central air cushion element 12 is also fastened to an encircling rim element 14. Thereby the rim element 14 encircles or surrounds the central air cushion element 12, which encircling may be a radial encircling in relation to the central axis AX.

As can also be seen, the air cushion element 12 comprises an air cushion part 12A centred around the central axis AX. The air cushion part 12A is also joined to and encircled by a supported part 12B.

Furthermore, the air cushion element 12 may also comprise a first fastening part 12C joined to the supported part 12B.

The air cushion part 12A may have a first edge that faces inwards towards the central axis AX and a second edge that is joined to a first edge of the supported part 12B. The first fastening part may in turn have a first edge that is joined to a second edge of the supported part. Thereby the first fastening part 12C may be joined to the air cushion part 12A via the supported part 12B.

The rim element 14 comprises a supporting part 14A of annular shape, a second fastening part 14B joined to the supporting part 14A and an optional concealing part 14C joined to the second fastening part 14B. Thereby the concealing part 14C may be joined to the supporting part 14A via the second fastening part 14B.

The supporting part 14A may have a first edge that faces inwards towards the central axis AX. A first edge of the second fastening part 14B may be joined to a second edge of the supporting part 14A. The concealing part 14C may in turn have a first edge joined to a second edge of the second fastening part 14B. The second fastening part 14B may also be angled away from the supporting part 14A with an angle of between ninety and one hundred and twenty degrees.

The rim element 14 is made of a first material and the air cushion element 12 comprises a second material, where the first material has a first GSM value and the second material has a second lower GSM value, where GSM is an abbreviation for grams per square meter. The second GSM value is thus lower than the first GSM value. It is additionally possible that the first GSM value is above 600 g/m² and the second GSM value is below 600 g/m². It is additionally possible that the second GSM value is below 500 g/m². It may as an example be about 420 g/m². It is furthermore possible that the first GSM value is above 800 g/m². It may as an example be about 890 g/m².

The second material may additionally be a cloth, for instance in the form of a web of woven strands of fibre material. The cloth may for instance be a nylon, cotton or silk cloth. The cloth may have an air permeability that is above 100 and below 4001/ (m²*s). It may for instance be an air permeability of 200 l/(m²*s).

The first material maybe a material in a group of non-hard plastic and/or rubber materials comprising or consisting of a thermoplastic elastomer (TPE) like thermoplastic polyurethane (TPU), a thermoplastic rubber (TPR), polyurethane (PU), styrene-butadiene rubber (SBR) and polyvinylchloride (PVC). The hardness of the first material may be a Shore A hardness of above 85 and below 98. The Shore A hardness may with advantage be a hardness of The throwing object io may have a first radius Ri, which may essentially be an outer radius of the supporting part 14A. The first radius Ri may be in the range 70 - 90 mm and may with advantage be 83.2 mm, while the air cushion part 12A of the air cushion element 12 may have a second radius R2, which may also be an inner radius of the supporting part 14A. The second radius may be in the range 40 - 85 and may with advantage be 52 mm. The first radius Ri may with advantage be in the range of 2.25 - 1.05 times larger than the second radius R2 and with advantage 1.6 times larger than the second radius R2.

The air cushion element 12 may have a first thickness Ti in the range of 1.5 - 2.1 mm and the first thickness Ti may with advantage be 1.8 mm, which first thickness Ti maybe the same throughout the whole air cushion element 12. The height H of the throwing object may be in the range 14 - 16 mm and may with advantage be 14.8 mm. The height H maybe in the range 6.6 - 10.7 higher than the first thickness Ti and with advantage 8.2 times higher than the first thickness Ti.

The rim element 14 may in turn have a thickness that varies. Starting from the first edge of the supporting part 14A that is radially closest to the axis AX and continuing to a second edge of the concealing part 14C via the second fastening part 14B, the thickness variation maybe the following:

The first edge of the supporting part 14A that is closest to the central axis AX may have a second thickness T2 at the second radius R2 of the air cushion part 12A. The second thickness T2 is a starting thickness of the rim element 14 where the supporting part 14A starts to support the supported part 12B. Thereafter the thickness increases in the direction towards the second fastening part 14B and at the point where the second edge of the supporting part 14A is joined to the first edge of the second fastening part 14B the rim element 14 has a third thickness T3 which may the maximum thickness of the whole rim element 14. Thereafter, in the second fastening part 14B, the thickness decreases to a fourth thickness T4 at the point where the second edge of the second fastening part 14B is joined to the first edge of the concealing part 14C, which is the lowest thickness of the rim element 14. The thickness then increases to a fifth thickness T5, which is the maximum thickness of the concealing part 14C and thereafter decreases to a sixth thicknessT6, which is the thickness at the second edge of the concealing part 14C.

The second thickness T2 may for instance be 2.8 mm, the third thickness T3 may for instance be 5.3 mm, the fourth thickness T4 may for instance be 0.6 mm and the sixth thickness T6 may for instance be 1.23 mm. The fifth thickness T5 may range between 5.0 and 13.5 mm and may with advantage be 5-3 mm.

The third thickness T3 at the point where the second edge of the supporting part 14A is joined to the first edge of the second fastening part 14B may be in the range 2 - 4 times larger than the first thickness Ti and with advantage 2.9 times larger than the first thickness Ti.

The cross-section of the combination of the supporting part 14A and the second fastening part 14B may be substantially L shaped, while the crosssection of the concealing part 14C may be substantially C- or boomerang shaped.

Before the throwing object 10 is assembled, the air cushion element 12 and rim element 14 are provided as separate elements.

During assembly, the air cushion element 12 is placed onto the rim element 14 so that the supported part 12B is located axially above the supporting part 14A. Thereby the supporting part 14A is located axially underneath the supported part 12B in the axial direction. Thus, the supporting part 14A is also being placed axially adjacent and in abutment with the supported part 12B. Thereby, the supported part 12B is aligned with and supported by the supporting part 14A, while the air cushion part 12A is unsupported as there is no part of the rim element 14 located underneath it. The first fastening part 12C is then placed over the second fastening part 14B and thereby the first fastening part 12C is also located radially outside the air cushion part 12A and the supported part 12B. Thereby the first and second fastening parts 12C, 14B are aligned with each other. The first fastening part 12C may additionally be angled away from the supported part 12B with the same angle that the second fastening part 14B is angled away from the supporting part 14A.

In order to tightly fasten the elements to each other, the first fastening part 12C may be fastened to the second fastening part 14B, such as through sewing or stitching. It should however be realized that other types of fastening may be used, such as gluing, heat pressing, etc. It is in this case also possible that the supported part 12B is fastened to the supporting part 14A, which may be done through for instance gluing.

After the first and second fastening parts 12C, 14B have been fastened to each other, the concealing part 14C may be folded over the second fastening part 14B and thereby the concealing part 14C also conceals the way fastening has been made between the first and second fastening parts 12C, 14B. The concealing part 14C may additionally be folded over the second fastening part 14B around the point where the second edge of the second fastening part 14B is joined to the first edge of the concealing part 14C.

Thereby a throwing object is obtained where an inner volume is defined by the air cushion part 12A, the supporting part 14A and the second fastening part 14B. The air cushion part 12A, the supporting part 14A and the second fastening part 14B each has an inner surface facing this inner volume and an outer surface facing away from the inner volume. Also the concealing part 14C has an inner and an outer surface, where the inner surface is the surface that faces the inner volume after folding has been performed and the outer surface is the surface that faces away from the inner volume after folding has been performed. It can also be seen that after folding, one end of the C or boomerang that forms the first edge of the concealing part 14C is joined to the second edge of the second fastening part 14B and another end of the C or boomerang that forms the second edge of the concealing part 14C abuts the air cushion element 12 at the point where the supporting part 14A joins the second fastening part 14B, i.e. at the position where the supported part 12B joins the first fastening part 12C. Moreover, when the concealing part 14C has been folded over the second fastening part 14B, the outer surface of the concealing part 14C may be flush or aligned with the outer surface of the supporting part 14A at the point where the supporting part 14A joins the second fastening part 14B.

Thereby, the first fastening part 12C may also be seen as being placed between the second fastening part 14B and the concealing part 14C. The first fastening part 12C may thereby be located in a cavity formed between the second fastening part 14B and the concealing part 14C when the concealing part 14C is folded over the second fastening part 14B.

The second fastening part 14B and the concealing part 14C of the rim element 14 may after the assembly together have a cross-section shaped as an ear. The throwing object 10 realized in this way has a very thin and light air cushion element 12 combined with a stable rim. This improves the ability of the object 10 to stay long in the air. Through the design of the rim element 14, the object 10 can at the same time be firmly gripped and accurately thrown. The rim element 14 also gives the object 10 good aerodynamic properties allowing a stable flight and makes the object 10 less inclined to wobble in the air.

When the object 10 is being thrown an air cushion may lift the air cushion part 12A, which, as can be seen in fig. 1 and 3, may also raise the supported part 12B and the supporting part 14A of the rim element 14 so that the shape of the supporting part 14A changes to the shape of a truncated cone. In this way the good aerodynamic properties are further enhanced. The throwing object with one or more of the above-mentioned properties has a number of advantages, Through the provision of the rim element 14 of the first material, the throwing object 10 does not collapse inwards when thrown in the air and thereby the rotation and the glide of the object is improved. The rim element 14 thus improves the stability of the throwing object 10 in air. The use of the second material has the advantage of lowering the weight and thereby it can glide in the air longer than if the throwing object was solely made up of the first material.

Furthermore, through the second fastening part 14B and the concealing part 14C forming a cavity in which the air cushion element 12 is fastened to the rim element 14, it is ensured that the way that fastening is made between the first fastening part 12C of the air cushion element 12 and the second fastening part 14B of the rim element 14 does not influence the performance in the air. The fastening between these two parts can thereby be made in an effective way with a limited consideration of the way that the throwing object behaves in air.

There are a number of variations that maybe made to the invention apart from those already disclosed. The size of the supported and supporting elements may vary. The second radius R2 may for instance be considerably higher than the above-mentioned advantageous value. It is also possible that the concealing element has a different shape. It may for instance be shaped so that the cavity is smaller. The cavity may for instance be shaped as a slot in which the first fastening part fits. Thereby the fifth thickness may be significantly higher than the above-mentioned advantageous thickness. It may for instance be about 2.5 times thicker than the above-mentioned advantageous thickness. It is also possible that there is no concealing part, in which case the ear shape is provided by the second fastening part alone and the outer surface of the second fastening part is aligned with the outer surface of the supporting part.

Furthermore, in the example given above, the second material was the only material of the air cushion element. As an alternative it is possible that the air cushion element comprises a number of layers, where the second material is one of the layers. Another layer may in this case be a plastic/and or rubber material layer, for instance of the same type as the first material or of another material, like another material in the above-mentioned group of materials. This other material may with advantage be softer than the first material

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

1. A disc shaped throwing object (io) comprising a central air cushion element (12) centred around a central axis (AX) and fastened to an encircling rim element (14), wherein the rim element (14) is made of a first material and the central air cushion element (12) comprises a second material, where the first material has a first GSM value and the second material has a second lower GSM value.

2. The disc shaped throwing object (10) according to claim 1, wherein the first GSM value is above 600 grams per square meter and the second GSM value is below 600 grams per square meter.

3. The disc shaped throwing object (10) according to claim 2, wherein the second GSM value is below 500 grams per square meter.

4. The disc shaped throwing object (10) according to claim 2 or 3, wherein the first GSM value is above 800.

5. The disc shaped throwing object (10) according to any previous claim, wherein the second material has an air permeability that is above 100 and below 4001/ (m²*s).

6. The disc shaped throwing object (10) according to any previous claim, wherein the second material is a cloth, for instance of nylon, cotton or silk.

7. The disc shaped object (10) according to any previous claim, wherein the air cushion element (12) comprises a number of layers, where said second material is one of the layers.

8. The disc shaped throwing object (10) according to any previous claim, wherein the first material is material in a group of non-hard plastic and/or rubber materials, comprising a thermoplastic elastomer (TPE) like thermoplastic polyurethane (TPU), a thermoplastic rubber (TPR), polyurethane (PU), styrene-butadiene rubber (SBR) and polyvinylchloride (PVC).

9. The disc shaped throwing object (10) according to any previous claim, wherein the first material has a Shore A hardness of above 85 and below 98 and with advantage a Shore A hardness of 95.

10. The disc shaped throwing object (10) according to any previous claim, wherein the air cushion element (12) comprises an air cushion part (12A) centred around said axis (AX) and joined to a supported part (12B) and the rim element comprises a supporting part (14A) of annular shape being placed axially adjacent and in abutment with the supported part (12B).

11. The disc shaped throwing object (10) according to claim 10, wherein the air cushion element (12) comprises a first fastening part (12C) joined to the supported part (12B) and the rim element (14) comprises a second fastening part (14B) joined to the supporting part (14) and where the first fastening part (12C) is fastened to the second fastening part (14B).

12. The disc shaped throwing object (10) according to claim 11, wherein the rim element (14) comprises a concealing part (14C) joined to the second fastening part (14B) and the concealing part (14C) is folded over the second fastening part (14B) so that the first fastening part (12C) is fastened to the second fastening part (14B) in a cavity of the rim element (14) formed between the second fastening part (14B) and the concealing part (14C) when the concealing part (14C) is folded over the second fastening part (14B).

13. The disc shaped throwing object (10) according to any previous claim, wherein the second material has a first thickness (Ti) in the range of 1.5 - 2.1 mm and with advantage of 1.8 mm.

14. The disc shaped throwing object (10) according to claim 13, wherein the throwing object has a height (H) in the range 14 - 16 mm and with advantage of 14.8 mm, which height (H) is in the range 6.6 - 10.7 higher than the first thickness (Ti) and with advantage 8.2 times higher than the first thickness (Ti). The disc shaped throwing object (10) according to claim 13 or 14 when depending on claim 11, wherein the rim element (14) has a thickness (T3) at the point where the supporting part (14A) is joined to the second fastening part (14B), which thickness (T3) is in the range 2 - 4 times larger than the first thickness (Ti) and with advantage 2.9 times larger than the first thickness (Ti).