The present invention relates to a fixing element, in particular to a fixing element for a drywall board.

In modern construction buildings are formed with an underlying structure, such as walls (2), wooden frameworks and ceiling structures, for example a ceiling framework. The interior surfaces of the underlying structure, are then lined with board (4) so as to form a drywall optionally with a space or cavity between the board and the underlying structure. For example, the wall (2) might be constructed from thermal blocks or breeze blocks and the board (4) might be plaster board. In addition ceilings may be lined with such boards, in which case the boards are fixed to an underlying ceiling frame or substrate.

Drywall fixing elements are used to fix the board to the wall or other underlying structure. In addition fixing elements are used to fix various attachment elements such as brackets, for example for shelves or cupboards, or picture hooks, etc. to the board. As the board may not be strong enough to support such attachment elements when they are loaded, for example when they are supporting a shelf or cupboard, with items arranged on or within it, fixing elements are sometimes used which pass through the board and fix into the underlying structure.

According to the present invention, there is provided a fixing element suitable for a wall arrangement comprising a drywall board, comprising: a tubular shaft having an insertion end and a proximal end remote from the insertion end, in which a portion of the tubular shaft adjacent the insertion end is formed with at least one pair of substantially longitudinal slots open at the insertion end defining at least one fin therebetween; and an internally threaded tubular wedge slideably and non-rotatably mounted within a portion of the tubular shaft adjacent the insertion end; wherein drawing of the tubular wedge towards the proximal end of the tubular shaft causes the wedge to move the or each fin outwardly. Thus, with the insertion end of the tubular shaft of the fixing element located within a hole formed in a board or in an underlying structure outward movement of the or each fin fixes the fixing element within such a hole. Preferably, there are at least two pairs of longitudinal slots defining at least two and preferably four fins.

The fixing element may additionally comprise an externally threaded screw element inserted into the proximal end of the tubular shaft and engageable with the internal thread of the wedge so as to draw the tubular wedge towards the proximal end of the tubular shaft on rotation of the screw element. Then with the screw element inserted into the proximal end of the shaft such that the threaded shaft engages the internal threads of the wedge and with the screw element held against longitudinal movement, rotation of the screw element draws the wedge towards the proximal end of the shaft. The tubular shaft may include an abutment surface for engaging a portion of the screw element so as to hold the screw element against longitudinal movement. For example, the abutment surface may be the proximal end of the tubular shaft. The externally threaded screw may comprise an enlarged head and a shaft where at least a portion of the shaft remote from the head is externally threaded. The screw element may be held against longitudinal movement by engagement of the screw element with the tubular shaft, for example by engagement of the head of the screw element with the proximal end of the tubular shaft, or another element such as a section of board or an attachment element, etc.

A portion of the shaft adjacent the insertion end may be formed with at least one slot and the wedge may be formed with at least one projecting element slideably engageable with a corresponding slot. In particular, the projecting elements may be slideably located within the open slots so as to rotationally fix the wedge within the shaft. This prevents relative rotation of the wedge within the shaft so that rotation of a screw element draws the wedge towards the proximal end of the shaft.

For example, a portion of the tubular shaft adjacent the insertion end may be formed with at least one substantially longitudinal slot open at the insertion end so as to enable the portions of the shaft between the slots to move outwardly on movement of the wedge towards the proximal end of the shaft. In particular, the projecting elements may be slideably located within the open slots so as to hold the wedge non-rotatably within the shaft. In this case the open slots have the dual purpose of preventing rotation of the wedge and facilitating the outward movement of the portion of the shaft adjacent the insertion end. At least a part of the external surface of the wedge may taper from a smaller diameter to a larger diameter in a direction towards the insertion end. For example the wedge may taper smoothly or may be formed with one or more tapered transition surfaces connecting different external diameter regions of the wedge. Also, at least a part of the internal surface of the tubular shaft adjacent the insertion end of the shaft may taper from a smaller diameter to a larger diameter towards the insertion end. Again the shaft may taper smoothly or may be formed with one or more tapered transition surfaces connecting different internal diameter regions of the shaft. The tapers of the wedge and the shaft may correspond to each other so that the tapered outer surface or surfaces of the wedge abuts the tapered internal surface or surfaces of the shaft in the unfixed position.

The shaft may comprise an outwardly extending collar at its proximal end for abutting a section of board so as to prevent the shaft from moving too far into a hole in a board.

The shaft may be made of a resilient material.

The fixing element may be an extended fixing element having an extended shaft wherein the length of the longitudinal slots is less than a half or less than a third of the length of the shaft. The extended shaft enables the fixing element to straddle any gap between a board and an underlying structure so as to enable fixing of the fixing element to the underlying structure. This provides a fixing which can be used to connect the board to the underlying structure or which can be used to fix weight bearing attachment elements, such as brackets.

The fins may form a primary expansion zone and a portion of the tubular shaft adjacent the proximal end may be formed with at least one U-shaped slot, with the base of the U-shape facing away from the proximal end and wherein the or each U-shaped slot defines a secondary fin, such that drawing of the tubular wedge towards the proximal end of the tubular shaft causes the wedge to move the or each secondary fin outwardly. The secondary fins may define a secondary expansion zone. Then when the fixing element is fixed within a hole through a section of board and an underlying structure, the primary expansion zone, comprising the fins may engage a part of the hole in the underlying structure and the secondary expansion zone, comprising the secondary fins may engage a part of the hole in the section of board.

Where there are two expansion zones, the tubular wedge may be formed with a first tapered transition surface on its external surface for engaging the fins and a with a second tapered transition surface on its external surface for engaging the secondary fins and the tapered transition surfaces taper from a smaller diameter to a larger diameter in a direction towards the insertion end. Similarly, the tubular shaft may be formed with a third tapered transition surface on its internal surface for engaging a portion of the tubular wedge and with a fourth transition surface on its internal surface for engaging a portion of the tubular wedge and the third and fourth transition surfaces taper from a smaller diameter to a larger diameter towards the insertion end. In particular, the third tapered transition surface may be located at the insertion end of the fins and the fourth tapered transition surface may be located at the insertion end of the secondary fins. The first and third tapered transition surfaces engage and the second and fourth tapered transition surfaces may engage to push the fins and the secondary fins outwardly.

At least one engaging element formed on the external surface of the tubular shaft. The or each engaging element may engage an internal surface of a hole within which it is fitted. For example, each engaging element may comprise a projecting element which forms and engages a corresponding recess in an internal surface of such a hole so as to prevent rotation of the fixing element within the hole. The or each engaging element may be located on a portion of the tubular shaft adjacent the insertion end thereof. In addition or alternatively, the engaging elements comprise a set of circumferential ribs in the regions of the fins and/or the secondary fins.

The tubular wedge may be rotationally fixed within the tubular shaft by virtue of a region of the internal surface of the tubular shaft having an irregular cross-section and a corresponding region of the external surface of the tubular wedge having a matching irregular cross-section. For example, the cross- sections may be partially circular and partially flat, for example a chord surface. The shaft of the or the wedge may comprise a key region and the other of the shaft or the wedge may comprise a keyway region, engageable on insertion of the wedge into the shaft so as to prevent relative rotation of the wedge and the shaft. The key and keyway may extend in a longitudinal direction so as to facilitate the wedge being slideable longitudinally within the shaft.

In one example of the present invention, the fixing element may be truncated, in which case it may have a truncated shaft wherein the length of the longitudinal slots is at least two thirds, preferably at least three quarters of the length of the shaft. The truncated fixing element may be fixed to a board so as to support various attachment elements, which do not bear significant weight.

The present invention also provides a method of fixing an extended fixing element to a wall arrangement comprising a board and an underlying structure comprising the step of passing the fixing element through a hole in the board and locating the insertion end of the fixing element in a hole in the underlying structure and then drawing the wedge towards the proximal end of the shaft so as to cause the fins to move outwardly so as to engage the hole in the underlying structure.

There is also provided a method of fixing a truncated fixing element to a board comprising the step of locating the fixing element in a hole in the board with the insertion end innermost and then drawing the wedge towards the proximal end of the shaft so as to cause the fins to move outwardly so as to engage the hole in the board. Further, there is provided method of fixing a fixing element having two expansion zones into a wall arrangement comprising a board and an underlying structure comprising the steps of passing the fixing element through a hole in the board and locating the insertion end of the fixing element in a hole in the underlying structure and then drawing the wedge towards the proximal end of the shaft so as to cause the fins to move outwardly so as to engage the hole in the underlying structure and the secondary fins to move outwardly so as to engage the hole in the board.

These methods may additionally comprise the steps of inserting a screw element into the proximal end of the shaft, engaging the external thread of the screw element with the internal thread of the wedge and rotating the screw element so as to draw the wedge towards the proximal end of the shaft.

The shaft may be made of a resilient material so as to facilitate outward movement of the portion of the shaft adjacent the insertion end.

An inwardly extending lip may be located at the insertion end of the shaft for securing the wedge within the shaft before use of the fixing element.

The present invention also provides a method of forming a fixing element, comprising the steps of: forming a tubular shaft having an insertion end and a proximal end remote from the insertion end; and slideably and non-rotatingly mounting an internally threaded tubular wedge within a portion of the tubular shaft adjacent the insertion end; wherein drawing of the tubular wedge towards the proximal end of the tubular shaft causes the wedge to move at least a portion of the tubular shaft adjacent the insertion end outwardly. In this case, the method may additionally comprise inserting an externally threaded screw element into the proximal end of the tubular shaft, engaging the external thread of the screw element with the internal thread of the wedge and rotating the screw element so as to draw the tubular wedge towards the proximal end of the tubular shaft.

The invention will now be described by way of example only and with reference to the accompanying schematic drawings, wherein:

Figure 1 shows a partial longitudinal cross-section through an extended fixing element according to the present invention extending between a section of board and an associated section of an underlying structure;

Figure 2 shows a longitudinal cross-section through a tubular shaft of the fixing element of Figure 1 ;

Figure 3 shows an insertion end view of the tubular shaft of Figure 2;

Figure 4a shows a proximal end view of a tubular wedge of the fixing element of Figures 1 and 6;

Figure 4b shows a longitudinal cross-section of the tubular wedge of Figure 4a;

Figure 4c shows an insertion end view of the tubular wedge of Figure 4a; Figure 5 shows a side view of an alternative tubular wedge of the fixing element of Figures 1 and 6; Figure 6 shows a longitudinal cross-section through a truncated fixing element according to the present invention;

Figure 7 shows an insertion end view of a tubular shaft of the fixing element of Figure 6;

Figure 8 shows a longitudinal cross-section of the tubular shaft of Figure 7; Figure 9 shows a longitudinal cross-section through a fixing element according to a second aspect of the present invention, having two expansion zones in an unfixed position;

Figure 10 shows a partial longitudinal cross-section of the fixing element of Figure 9 in a fixed position, extending between a section of board and an associated section of an underlying structure;

Figure 1 1 shows a longitudinal cross-section through a tubular shaft of the fixing element of Figure 10;

Figure 12 shows a side view of a tubular wedge of the fixing element of Figure 10;

Figure 13 shows a transverse cross-section through the tubular wedge of Figure 12, taken at section AA of Figure 12;

Figure 14A shows a transverse cross-section through the tubular shaft of Figure 1 1 , taken at section BB of Figure 1 1 ; and

Figure 14B shows a transverse cross-section through the tubular shaft of Figure 1 1 , taken at section CC of figure 1 1 .

Figure 1 shows a section of a wall (2) of a building, for example, constructed from breeze block, which is lined on its internal surface, ie. the room side of the wall, with a section of board (4), for example plaster board. Generally, there will be a cavity (6) between the board (4) and the underlying section of wall (2).

The extended fixing element (8) shown in Figure 1 can be used to fix the board (4) to the underlying wall (2) or it can be used to fix an attachment element, such as a bracket (10) to the board. As the board (4) tends to be quite weak, the extended fixing element (8) passes through the board (4), straddles the cavity (6) and fixes into the underlying wall (2).

The extended fixing element comprises an extended tubular shaft (12), which is shown in more detail in Figures 2 and 3. The tubular shaft (12) has an insertion end within which is formed at least one, in this example four, longitudinal slots (14) which extend substantially parallel to a longitudinal axis of the shaft (12). The slots (14) extend for approximately one third of the length of the tubular shaft (12) from the insertion end. At least one engaging element, formed as a longitudinal rib (16) extends outwardly of the external surface of the tubular shaft (12) along at least a slotted portion of the tubular shaft formed with the slots (14). The or each rib (16) extends substantially parallel to the longitudinal axis of the shaft (12). In this example, there are four ribs (16), interspersed between the four slots (14). In the example shown in Figures 1 to 3, the external surface of the tubular shaft (12) is a right cylinder and the ribs extend at an angle a to a radius (r) of the cylinder, with each rib extending at substantially the same angle to an adjacent radius of the cylinder. A radially inwardly extending lip (30) terminates the insertion end of the tubular shaft (12). The internal surface (32) of the slotted portion of the tubular shaft (12) tapers smoothly outwardly from a smaller internal diameter at a base (34) of the slots to a larger diameter towards the lip (30) of the insertion end. At the proximal end of the shaft (12) remote from the slotted insertion end, the tubular shaft is formed with an annular radially outwardly extending collar (18).

The extended fixing element of Figure 1 additionally comprises a tubular tapered wedge (20), a first example of which is shown in Figures 4a to 4c. The wedge (20) has an internal substantially cylindrical threaded surface (22). The internal thread in this example is suitable for engagement with an external thread of a parallel threaded screw (24), shown in Figure 1 . The wedge (20) has an external surface which smoothly tapers radially outwardly from a first proximal end (24) of the wedge to a second insertion end (26) of the wedge. A view from the proximal end of the wedge (20) is shown in Figure 4a and a view from the insertion end of the wedge is shown in Figure 4c. The insertion end (24) of the wedge (20) is formed on its outer surface with at least one substantially radially outwardly extending rib (28). The ribs (28) correspond to the slots (14) of the tubular shaft (12) so that each rib (28) is slideably locatable with a corresponding slot (14) in the tubular shaft so as to hold the tubular wedge (20) against rotation within the tubular shaft (12). Thus, in this example, four ribs (28) are formed on the wedge (20).

An alternative design of wedge (20') is shown in Figure 5, with like parts labelled by like numerals. The only difference between the wedge (20) of Figures 4a to 4c and the wedge (20') of Figure 5 is that the wedge (20') of Figure 5 is formed with an internal thread suitable for receiving a self-tapping screw.

The extended fixing element (12) is fixed in place by inserting a screw element (24) into the proximal end of the shaft (12) and engaging an externally threaded insert end (36) of the screw element with the internal thread of the wedge (20). The screw element (24) has a proximal end at which is located a head (38) of the screw element. The end face (40) of the screw element is formed with a recess shaped to receive a correspondingly shaped tip of a screw driving tool, such as a hand held screwdriver or a driving tool of a powered screwdriver or drill/driver. For example, the recess in the face (40) may be formed as a slot, suitable for receiving a blade tipped screwing tool or as a cross, suitable for receiving a cross-head or Phillips screwing tool. Other such recess formations are known in the art for receiving correspondingly formed screwing tools. In Figure 1 , the screw element (24) has an extended shaft (42) with is externally threaded along its entire length, however, only the insertion end portion of the extended shaft which engages the wedge (20) need be threaded. The length of the extended shaft (42) of the screw element is set so that the shaft (42) can pass through the extended tubular shaft (12) of the fixing element and engage at least a portion of the internal thread of the wedge (20) to fix the fixing element (8) in place. When the fixing element (8) is fixed in place the head of the screw (38) abuts the bracket (10) so as to hold the bracket in place. In Figure 1 the screw element (24) is formed with a parallel thread suitable for engagement with the wedge (20) of Figures 4a to 4c. Where the fixing element (8) has a wedge (20') of Figure 5, the screw element (24) is formed with a self tapping thread.

The fixing element of Figure 1 is formed by pushing the smaller external diameter proximal end (24) of the wedge (20, 20') into the insertion end of the extended shaft (12). The ribs (28) of the wedge (20, 20') are aligned with and then passed into the slots (14) of the tubular shaft (12). The wedge (20, 20') is passed into the shaft (12) until the tapered external surface of the wedge (20, 20') abuts the correspondingly tapered internal surface at the insertion end of the shaft (12) and the insertion end (26) of the wedge (20, 20') passes the internal lip (30) of the shaft (12). The slots (14) in the insertion end of the shaft enable the portions of the shaft or fins in between the slots to move radially outwardly so as to accommodate the wedge (20, 20') until the wedge passes the lip (30). Accordingly, the insertion end of the shaft (20) is made of a material which is suitably resilient. The internal lip (30) holds the wedge (20, 20') within the insertion end of the shaft (12) and the abutting tapered surfaces of the insertion end of the shaft (12) and the wedge (20, 20') hold the wedge in the insertion end of the shaft in the unfixed position shown in Figure 1 .

The extended fixing element (8) is fixed in place by firstly, forming a hole, for example by drilling, through the board (4) and then beyond that into the wall (2). The insertion end of the fixing element (8) is then pushed through the hole in the board (4), across the cavity and then into the hole in the wall (2), until the collar (18) at the proximal end of the tubular shaft (12) abuts the internal face of the board (4), ie. into the position shown in Figure 1 .

If it is intended to fix an attachment element such as a bracket (10) to the board (4) then a through hole (44) of the bracket is placed over the open proximal end of the shaft (12) with the collar (18) of the shaft between the bracket (10) and the board (4). Then an insertion end (36) of the shaft (42) of the screw element (24) is passed through the hole (44) of the bracket (10) and along the tubular shaft (12) until the insertion end of the screw element is adjacent to the proximal end (24) of the wedge (20, 20'). If it is intended to fix the board (4) to the wall (2) then no bracket (10) is required and the insertion end (36) of the screw element (24) is passed into the tubular shaft (12) until the insertion end of the screw element is adjacent to the proximal end (24) of the wedge (20, 20'). The hole formed in the wall (2) is sized so that as the insertion end of the shaft (12) is pushed or hammered into the hole, the ribs (16) formed on the insertion end of the shaft form and engage longitudinal ridges in the hole in the wall, so that the shaft (12) is constrained against rotation with respect to the wall (2).

Then the screw element (24) is rotated, for example by engaging the tip of a screw driving tool with the recess in the head (38) of the screw element so that the external thread at the insertion end (36) of the screw element engages the internal thread within the proximal end (24) of the wedge (20, 20'). The wedge (20, 20') is constrained against rotation by the engagement of the ribs (28) of the wedge with the corresponding slots (14) of the tubular shaft (12) and by engagement of the ribs (16) of the shaft (12) with the wall (2). Then with the screw element (24) held against longitudinal movement, rotation of the screw element draws the wedge (20, 20') towards the proximal end of the shaft (12). The tubular shaft (12) includes an abutment surface formed by the proximal end of the tubular shaft so as to facilitate holding of the screw element against longitudinal movement, indirectly by engagement of the head (38) of the screw element (24) with the bracket (10) which abuts the annular collar (18) at the proximal end of the shaft (12).

Thus, rotation of the screwing element draws the wedge (20, 20') in the direction of the proximal end of the shaft (12), ie. in the direction of the arrow in Figure 1 . As the wedge (20, 20') is drawn further into the shaft (12) the engagement of the tapered external surface of the wedge with the slotted insertion end of the shaft (12) causes the fins formed between the slots at the slotted insertion end of the shaft to expand outwardly so as to fix the insertion end of the fixing element securely within the hole in the wall (2). Where the fixing element (8) is used to fix a bracket (10) to a board (4), the screw element (24) is rotatingly driven into the tubular wedge (20, 20') with the head (38) abutting the bracket (10) so as to secure the bracket in place. Where the fixing element (8) is used to fix a board (4) to an underlying structure (2), the screw element (24) is rotatingly driven into the tubular wedge (20, 20') with the head (38) abuting the annular collar (18) of the tubular shaft (12).

Figures 6 to 8 shows an alternative embodiment of a truncated fixing element (108) which is similar to the embodiment discussed above in relation to Figures 1 to 5, with like parts identified by like numerals. The main difference is that the tubular shaft (1 12) of Figures 6 to 8 is truncated and the tubular shaft (1 12) does not have a collar at its proximal end. The length of the tubular shaft (1 12) is slightly longer than the length of the wedge (20). The wedge (20) of Figures 4a to 4c or the wedge (20') of Figure 5 is used in the fixing element (108) of the embodiment of Figures 6 to 8.

The fixing element of Figures 6 to 8 is used for fixing various attachment elements, such as brackets, picture hooks, etc. to the board (4). As the fixing element of Figures 6 to 8 does not fix into the underlying structure, but instead fixes into the board (4) it is not able to support as high a load as the fixing element of Figures 1 to 5. The screw element used in relation to the fixing element (108) has a short externally threaded shaft. The head of the screw element can abut a bracket, such as bracket (10) when it is screwed into the fixing element (108) so that the bracket is fixed between the head of the screw fixing and the board (4).

Firstly, a suitably sized hole is formed in the board (4). The hole formed in the board (4) is sized so that as the truncated shaft (1 12) is pushed or hammered into the hole, the fins (16) formed on the shaft form and engage longitudinal ridges in the hole in the board (4), so that the shaft (1 12) is constrained against rotation with respect to the board (4).

The screw element is then positioned ready for its insertion end to be screwed into the wedge (20) and with the head of the screw element abutting for example, the proximal end of the shaft (1 12). Then the screw element is rotated so that the external thread at the insertion end of the screw element engages the internal thread within the proximal end (24) of the wedge (20, 20'). The wedge (20, 20') is constrained against rotation by the engagement of the ribs (28) of the wedge with the corresponding slots (14) of the tubular shaft (1 12) and by engagement of the ribs (16) of the shaft (1 12) with the board (4). Thus, rotation of the screw element, which is constrained against longitudinal movement, draws the wedge (20, 20') in the direction of the proximal end of the shaft (1 12), ie. in the direction of the arrow in Figure 6. As the wedge (20, 20') is drawn further toward the proximal end of the shaft (1 12) the engagement of the tapered external surface of the wedge with the slotted insertion end of the shaft causes the fins defined by the longitudinal slot (14) in the slotted insertion end of the shaft to expand outwardly so as to fix the fixing element securely within the hole in the board (4). Where the fixing element (8) is used to fix a bracket (10) to a board (4), the screw element is driven into the fixing element (108) with the head of the screw element abutting the bracket (10) so as to secure the bracket in place.

The tubular shaft (12,1 12) and/or the tubular wedge (20,20') may be made from a metal, such as steel. In particular, the tubular shaft is made of a resilient material. Other metals are known in the art for making such fixing elements. Alternatively, the tubular shaft (12,1 12) and/or the tubular wedge (20,20') may be made from plastic, examples of which are well known in the art. Figures 9 to 14 show an alternative embodiment of the extended fixing element of Figures 1 to 5, which comprises two expansion zones, a primary expansion zone at the insertion end of the fixing element, for engaging an underlying structure (2), as is described above in relation to Figures 1 to 5 and a secondary expansion zone towards the proximal end of the fixing element, for engaging a section of board (4), as is shown in Figure 10.

A tubular shaft (50) of the embodiment of Figures 9 to 14 is shown in longitudinal cross-section in Figure 1 1 . The tubular shaft is formed with a radially outwardly extending collar (52) at its proximal end, for abutting a front face of a section of board (4), as is shown in Figure 10. At its insertion end the tubular shaft (50) is formed with four longitudinal slots, spaced equally around the circumference of the tubular shaft so as to define four primary fins (54) forming the primary expansion zone, in a similar way as is described above in relation to the slots (14) of the tubular shaft (12) of the embodiment of Figures 1 to 5. At the end of the insertion end of the tubular shaft (50), the internal surface of the shaft is outwardly tapered from a diameter (D1 ) to a wider diameter at the end, forming a tapered transition surface (88).

Towards its proximal end the tubular shaft (50) is formed with two opposing U- shaped slots (56), defining two opposing secondary fins (58), forming the secondary expansion zone, as is shown in Figures 1 1 and 14B.

The external surface of the tubular shaft (50) in the region of the primary and secondary expansion zones are formed with engaging elements in the form of a plurality of circumferential engaging ribs (60). A section on the tubular shaft (50) between the expansion zones is not formed with engaging elements.

The tubular shaft (50) has a first region adjacent the insertion end of the tubular shaft which has a substantially cylindrical internal cross-section D1 which extends along part of the primary fins (54). The shaft (50) has a second region, adjacent the first, which has an internal cross-section shown in Figure 14A, which comprises two opposing part cylindrical sections (64) of diameter D1 separated by two opposing chord-sections (62) separated by a distance of D2. As shown in Figure 1 1 , the chord-sections (62) are aligned with the regions between the secondary fins (58). The second region extends along the remainder of the primary fins (54) and along the central portion of the tubular shaft (50). The tubular shaft has a third region, adjacent the second, which extends along the secondary expansion zone and which has an internal cross-section shown in Figure 14B in which the cord-sections (62) continue into the region between the secondary fins (58) and in which the internal surfaces (90) of the secondary fins are part cylindrical with an internal diameter of D2, as is shown in Figure 14B.

The tubular shaft (50) has a fourth region adjacent the proximal end of the tubular shaft which has a substantially cylindrical internal cross-section D3, for receiving a screw or bolt (70). The distance D3 is less than the distance D2 and the distance D2 is less than the distance D1 . The internal surface of the shaft (50) also comprises a first pair of opposing tapered transition surfaces (68) at its transition between the first region of diameter D1 and the chord-sections (62) of the second region. The internal surface of the shaft (50) further comprises a second pair of opposing tapered transition surfaces (84), as shown in Figure 9, at its transition between the part cylindrical regions (64) of diameter D1 of the second region of the tubular shaft and the part cylindrical regions (90) of diameter D2 of the third region.

The fixing element of the embodiment of Figures 9 to 14 comprises a tubular wedge (66) as shown in Figures 12 and 13. The tubular wedge (66) has a substantially cylindrical internal cross-section, as is shown in Figure 14, having diameter D3 and the internal surface of the tubular wedge is internally threaded for receiving a bolt or screw (70).

The tubular wedge (66) is formed at its insertion end with an increased first external diameter insertion end region (72) with a diameter D4 greater than D1 . A proximal end region (74) of the tubular wedge (66) has a cross-section matching the internal cross-section of the central region of the tubular shaft (50), ie. two opposing part cylindrical surfaces (76) of diameter D1 in between two flat opposing chord-sections (78), spaced apart by distance D2, as shown in Figure 13. At the proximal end of the proximal end region of the tubular wedge, the part cylindrical surfaces (76) are formed with a proximal tapered transition surface (80) tapering from diameter D1 to diameter D2. The tubular wedge (66) is additionally formed with a tapered transition surface (82) between the insertion end region (72) and the proximal end region (74) of the wedge.

Figure 9 shows the fixing element of Figures 9 to 14 in an unfixed position. The fixing element comprises the tubular shaft (50) of Figures 1 1 and 14, the tubular wedge (66) of Figures 12 and 13 and the screw or bolt (70).

The tubular wedge (66) is rotationally fixed within the tubular shaft (50) by virtue of the proximal end region (74) fitting non-rotationally in the second region (50) of the tubular shaft, ie. due the engagement flat chord surfaces (62, 77) and the cylindrical surfaces (64, 76) (See Figures 14 and 14A) of the internal surface of the central portion of the tubular shaft and the external surface of the proximal end portion of the wedge, respectively. In Figure 9, the tapered transition surface (80) at the proximal end of the wedge (66) abuts the tapered transition surface (84) at the insertion end of the secondary fins (58), between the second and third regions of the tubular shaft (50). Also, the tapered transition surface (82) between the insertion end region (72) and the proximal end region of the tubular wedge (66) abuts the tapered transition region (88) at the insertion end of the tubular shaft (50).

The screw or bolt (70) is externally threaded and passes through the fourth region at the proximal end of the tubular shaft (50) and is screwed into the internally threaded tubular wedge (66). An annular metal washer (90) is located between annular collar (52) at the proximal end of the tubular shaft and a head of the screw (70). The screw or bolt (70) may be made of metal. A hole is drilled through a section of board (4) and into the underlying structure (4), just large enough for the fixing element, in its un-expanded state of Figure 9 to be fitted into the hole, with the annular collar (52) of the tubular shaft abutting a front face of the section of board.

Then the screw or bolt (70) is rotated, for example, using a screw driving device which engages the head of the screw (70) to drive it in rotation. The screw (70) is driven in a direction so as to cause the internally threaded tubular wedge (66) to move along the screw (70) towards the proximal end of the tubular shaft (50) and into the position shown in Figure 10.

In Figure 10, the abutting tapered transition surfaces (82,88) ride over each other as the tubular wedge (66) is forced by the rotation of the screw (70) (shown partly in dotted lines in Figure 10) to move towards the proximal end of the tubular shaft (50) so as to push the primary fins (54) outwardly to engage the sides of the hole drilled into the underlying structure (2), as shown in Figure 10. Simultaneously, the abutting tapered transition surfaces (80, 84) ride over each other so as to push the secondary fins (58) outwardly to engage the sides of the hole drilled into the section of board (4), as shown in Figure 10. Figure 10 shows the fixing element in the fixed position, in which the circumferential ribs on the external surface of the primary and secondary fins, firmly engage the sides of the holes drilled in the underlying structure (2) and section of board (4) respectively. This, provides an effective load bearing fixing element.