Technical Field

The present invention relates to self-drilling building panel fasteners, particularly, but not exclusively, self-drilling building panel fasteners for fastening insulated building panels to structural members.

Background

Conventionally, insulated (or composite) building panels are fixed to structural members such as purlins by fastening screws. The building panels commonly comprise two relatively thin sheet-like skin layers formed of metal, with a layer of insulation therebetween.

Conventionally, one type of self-drilling building panel fastener comprises a so-called high thread screw which includes a head and a shank, the shank extending from the head to a tip, the shank including, in sequence from the tip, a drill point, a structural member engaging threaded part, an unthreaded part and an outer panel layer engaging threaded part.

In use, the screw is drilled through the building panel into a steel structural member. The drill point drills a hole through the building panel and then drills a hole in the structural member, and the structural member engaging threaded part self-taps a thread in the hole in the structural member to fix the screw to the structural member. The outer panel layer engaging threaded part has a larger diameter dimension than the structural member engaging threaded part and as the structural member engaging threaded part is tapping the thread in the hole in the structural member, the outer panel layer engaging threaded part self-taps a slightly larger hole in the outer skin layer of the building panel. The thread formed in the hole in the outer skin layer of the building panel aids sealing and helps prevent leakage. A sealing arrangement comprising one or more washers is located between the head of the screw and the outer skin layer to resist rain penetration. The distance between the head and the structural member engaging threaded part is arranged to correspond with the thickness of the building panel, so that when correctly fitted, the panel is tightly held to the structural member but is not deformed.

One disadvantage of this arrangement is that if the screw is over-driven, two deleterious consequences can result. One consequence is that the thread formed in the outer skin layer strips, leading to leakage. A second consequence is that the outer skin layer and the insulation layer can be compressed and deformed, so that a depression forms around the head. The depression increases the risk of local ponding and/or pooling and can then lead to leaking of the building panel at the location of the fasteners.

In practice, both of these consequences occur together leading to a high likelihood of leakage occurring as a result of over-driving.

Over-driving occurs when the screw is driven too far into the structural member for the thickness of the building panel and the above consequences result. Over-driving can be avoided or its likelihood reduced by operator training and care during installation.

Over-driving can occur as a result of poorly trained operatives, poor working practices and/or poorly maintained equipment. Another factor is that, for economy, the material thickness of the upper and lower panel metal layers has been reduced over time, increasing the likelihood of stripping, deformation and therefore leakage. Such fasteners are commonly used on large warehouses which can require thousands of fasteners. Leakage of any significant proportion of the fasteners can result in stock loss and damage and require expensive remedial work.

Even with well trained and careful operators, there can be a mismatch between design specification and actual installation details which can result in poor installation, deformation and leakage. For example, the panels can vary in thickness and the structural members can bow.

In this specification, the term insulated building panels comprises: insulated building panels, cladding panels and wall panels; composite building panels, cladding panels and wall panels; and so-called sandwich panels.

In this specification, the following terms are used in relation to thread formations: i) major diameter dimension: the dimension of the major or outer diameter dimension of the thread formation; ii) pitch dimension: the axial length of one pitch or thread turn; iii) crest angle: the angle subtended in cross-section by the slopes of the thread formation at the crest or apex of the thread formation. In this specification, the start of a threaded formation is taken to be towards the tip of the fastener and the end towards the head.

Statements of Invention

According to a first aspect of the present invention, there is provided a self-drilling building panel fastener for fastening an insulated building panel to a structural member, the fastener including a head and a shank, the shank extending from the head to a tip, the shank including, in sequence from the tip, a drill part, a first threaded part, an indicator threaded part, an unthreaded part and a third threaded part,

wherein, in use during installation, the fastener is driven into the structural member and penetrates the structural member,

the indicator threaded part being arranged to provide an indication to a user that the fastener has reached a predetermined depth of penetration in the structural member.

Possibly, in use, the first threaded part threadably engages the structural member.

Possibly, in use, the third threaded part threadably engages the building panel.

Possibly, the indication is a tactile indication. Possibly, the indication is an audible indication. Possibly, the indication is both a tactile and an audible indication.

Possibly, in use during installation, when the indicator threaded part penetrates the structural member, a greater force is required to drive the fastener into the structural member.

Possibly, the first threaded part includes a first threaded formation, which may be constant in dimension along the first threaded part. Possibly, the indicator threaded part includes an indicator threaded formation. Possibly, the indicator threaded formation is different to the first threaded formation, so that the greater force is required to drive the fastener into the structural member.

Possibly, the first threaded formation has a first major diameter dimension. Possibly, the indicator threaded formation has an indicator major diameter dimension. Possibly, the indicator major diameter dimension is greater than the first major diameter dimension, so that the greater force is required to drive the fastener into the structural member. Possibly, the indicator threaded part abuts the first threaded part.

Possibly, the first threaded formation is a self-tapping threaded formation. Possibly, the first threaded formation has a first pitch dimension, and may have a first crest angle.

Possibly, the indicator threaded part includes a second threaded part. Possibly, the second threaded part includes a second threaded formation, which may be constant in dimension along the second threaded part, and may be a self-tapping threaded formation. Possibly, the second threaded formation is different in dimension to the first threaded formation. Possibly, the different dimension of the second threaded formation to the first threaded formation comprises the indication.

Possibly, the second threaded formation has a second major diameter dimension, and may have a second pitch dimension, and may have a second crest angle.

Possibly, the second major diameter dimension comprises the indicator major diameter dimension.

Possibly, in use during installation, when the indicator threaded part penetrates the structural member, the indicator threaded part does not cause the fastener to abruptly stop.

Possibly the indicator threaded part includes a transition threaded part.

Possibly, the transition threaded part is located between the first threaded part and the second threaded part.

Possibly, the transition threaded part includes a transition threaded formation, which varies in dimension along the transition threaded part.

Possibly, the change in dimension of the transition threaded formation comprises the indication.

Possibly, the transition threaded formation has a major diameter dimension, which may vary from the first major dimension at one end of the transition threaded part to the second major dimension at another end of the transition threaded part. Possibly, the transition threaded formation has a pitch dimension, which may vary from the first pitch dimension at one end of the transition threaded part to the second pitch dimension at another end of the transition threaded part.

Possibly, the transition threaded formation has a crest angle, which may vary from the first crest angle at one end of the transition threaded part to a or the second crest angle at another end of the transition threaded part.

Possibly, the second pitch dimension is substantially the same as the first pitch dimension.

Possibly, the second crest angle is substantially the same as the first crest angle.

Possibly, the driving of the fastener into the structural member includes a plurality of stages as different parts of the fastener drill or screw into or through the structural member.

Possibly, the stages include a first threaded part screwing stage, in which the first threaded part is screwing through the structural member. Possibly, the stages include a second threaded part tapping stage, in which the second threaded formation taps a second thread in the structural member hole.

Possibly, the second threaded part tapping stage requires the greater force to drive the fastener than the first threaded part screwing stage. Possibly, the second threaded part tapping stage provides the indication.

Possibly, the stages include a transition stage, in which the transition threaded part is screwing into the structural member. Possibly, the transition stage is between the first threaded part screwing stage and the second threaded part tapping stage.

Possibly, the third threaded part includes a third threaded formation, which may be a self tapping threaded formation. Possibly, the third threaded formation has a third major diameter dimension and may have a third pitch dimension and may have a third crest angle.

Possibly, the third major diameter dimension is greater than the second major diameter dimension. Possibly, the third pitch dimension is greater than the first pitch dimension and/or the second pitch dimension.

Possibly, the third crest angle is less than the first crest angle and/or the second crest angle.

Possibly, the shank extends lengthwise along a shank axis.

Possibly, the second threaded formation extends for a second length along the shank axis. The second length may be greater than 3.2 mm, and is desirably greater than 6.2 mm. Possibly, the second length is less than 13.2mm and is desirably less than 10.2mm.

Possibly, the transition threaded formation extends for a transition length along the shank axis. The transition length may be at least 1.5 times the first pitch dimension, may be no more than 2.5 times the first dimension, and may be substantially 2 times the first pitch dimension.

Possibly, the fastener includes an indication dimension, which may be the dimension between the start of the second threaded formation and the head, or the dimension between the end of the transition threaded formation and the head.

Possibly, in use, the fastener fastens the building panel to the structural member. Possibly, the building panel has a thickness. Possibly, the indication dimension is arranged to correspond with the building panel thickness.

Possibly, the indication dimension is at least as long as the building panel thickness and may be greater than the building panel thickness.

Possibly, the indication dimension includes an allowance dimension, which may be the axial length of penetration of the second threaded formation into the structural member in the design installed condition.

Possibly, the allowance dimension allows no less than one turn of the second threaded formation in the structural member hole, and may allow no less than 1.5 turns. Possibly, the allowance dimension allows no more than three turns of the second threaded formation in the structural member hole, and may allow no more than 2.5 turns. Possibly, the allowance dimension is no less than 1.8 mm and desirably is no less than 2.7 mm. Possibly, the allowance dimension is no more than 5.4 mm and desirably is no more than 4.5 mm.

Possibly, in use during installation, a sealing arrangement comprising a washer is located between the head of the fastener and the building panel.

Possibly, the building panel is any one from the group containing insulated building panels, cladding panels, wall panels; composite building panels, cladding panels and wall panels; and so- called sandwich panels.

Possibly, the building panel comprises two relatively thin sheet-like skin layers, with a layer of insulation therebetween. Possibly, the skin layers are formed of metal. Possibly, the skin layers include, in use during and after installation, an outer skin layer and an inner skin layer.

Possibly, the fastener comprises a screw.

Possibly, the structural member comprises a roof purlin. Possibly, the fastener is a roof panel fastener. Possibly, the structural member is formed of steel and may be formed of a box section, C section or Z section. The structural member may have a section thickness of 1 to 12 mm.

Possibly, in use during installation, the fastener is drilled through the building panel into the steel structural member. Possibly, in use, the drill part drills a hole through the building panel and then drills a hole in the structural member. Possibly, the first threaded part self-taps a thread in the hole in the structural member to fix the fastener to the structural member.

Possibly, in use during installation, as the first threaded part is tapping and/or screwing through the hole in the structural member, the third threaded part taps a thread in the hole in the outer skin layer of the building panel.

According to a second aspect of the present invention, there is provided a method of fixing an insulated building panel to a structural member, the method including providing a self-drilling building panel fastener, the fastener including a head and a shank, the shank extending from the head to a tip, the shank including, in sequence from the tip, a drill part, a first threaded part, an indicator threaded part, an unthreaded part and a third threaded part, wherein, in use during installation, the fastener is driven into the structural member and penetrates the structural member,

the indicator threaded part being arranged to provide an indication to a user that the fastener has reached a predetermined depth of penetration in the structural member.

Possibly, the fastener includes any of the features described in any of the preceding statements or following description. Possibly, the method includes any of the steps described in any of the preceding statements or following description.

Figures

An embodiment of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:-

Fig. 1 is a side view of a self-drilling building panel fastener, with dimensions labelled which are referenced in Table 1 ; and

Fig. 2 is a side schematic view of the fastener in an installed condition.

In the drawings, where multiple instances of the same or similar features exist, only a representative one or some of the instances of the features may have been provided with numeric references for clarity.

Description

Figs. 1 and 2 show a self-drilling building panel fastener 10 for fastening an insulated building panel 12 to a structural member 14. The fastener 10 includes a head 16 and a shank 20, the shank 20 extending from the head 16 to a tip 18.

The shank 20 includes, in sequence from the tip 18: a drill part 22, a first threaded part 30, an indicator threaded part 100, an unthreaded part 24 and a third threaded part 50.

In use during installation, the fastener 10 is driven into the structural member 14 and penetrates the structural member 14.

The indicator threaded part 100 is arranged to provide an indication to a user that the fastener 10 has reached a predetermined depth of penetration in the structural member 14. In use during installation, when the indicator threaded part 100 penetrates the structural member 14, a greater force is required to drive the fastener 10 into the structural member 14.

The indicator threaded part 100 abuts the first threaded part 30.

The first threaded part 30 includes a first threaded formation 32, which is a self-tapping threaded formation, and is constant in dimension along the first threaded part 30. The indicator threaded part 100 includes an indicator threaded formation 102. The indicator threaded formation 102 is different to the first threaded formation 32, so that the greater force is required to drive the fastener 10 into the structural member 14.

The first threaded formation 32 has a first major diameter dimension D1. The indicator threaded formation 102 has an indicator major diameter dimension 104. The indicator major diameter dimension 104 is greater than the first major diameter dimension D1 , so that the greater force is required to drive the fastener 10 into the structural member 14.

The first threaded formation 32 has a first pitch dimension P1 and a first crest angle 38.

The indicator threaded part 100 includes a second threaded part 40.

The second threaded part 40 includes a second threaded formation 42, which is a self tapping threaded formation, and is constant in dimension along the second threaded part 40. The second threaded formation 42 has a second major diameter dimension D2, a second pitch dimension P2, and a second crest angle 48.

The second major diameter dimension D2 comprises the indicator major diameter dimension 104.

In the example shown, the second major diameter dimension D2 is greater than the first major diameter dimension D1 and the second pitch dimension P2 is substantially the same as the first pitch dimension P1.

In the example shown, the second crest angle 48 is also substantially the same as the first crest angle 38. In use during installation, when the indicator threaded part 100 penetrates the structural member 14, the indicator threaded part 100 does not cause the fastener 10 to abruptly stop.

The indicator threaded part 100 includes a transition threaded part 28, which is located between the first threaded part 30 and the second threaded part 40.

The transition threaded part 28 includes a transition threaded formation 82, which is a self tapping threaded formation, and varies in dimension along the transition threaded part 28

The transition threaded formation 82 has a major diameter dimension which varies from the first major dimension D1 at one end of the transition threaded part 28 adjacent the first threaded part 30 to the second major dimension D2 at another end of the transition threaded part 28 adjacent the second threaded part 40.

The transition threaded formation 82 has a pitch dimension, which could vary from the first pitch dimension P1 at the one end of the transition threaded part 28 to the second pitch dimension P2 at the other end of the transition threaded part 28. In the example shown, the first pitch dimension P1 and the second pitch dimension P2 are the same, and the pitch dimension of the transition threaded formation 82 does not vary.

The transition threaded formation 82 has a crest angle, which could vary from the first crest angle 38 at the one end of the transition threaded part 28 to the second crest angle 48 at the other end of the transition threaded part 28. In the example shown, the first crest angle 38 and the second crest angle 48 are the same, and the crest angle of the transition threaded formation 82 does not vary.

The third threaded part 50 includes a third threaded formation 52, which is a self-tapping threaded formation. The third threaded formation 52 has a third major diameter dimension D3, a third pitch dimension P3 and a third crest angle 58.

The third major diameter dimension D3 is greater than the second major diameter dimension D2 and the first major diameter dimension D1. The third pitch dimension P3 is greater than the first pitch dimension P1 and the second pitch dimension P2. The third crest angle 58 is less than the first crest angle 38 and the second crest angle 48. The third threaded part 50 is close to or abuts the head 16. In some examples the third threaded part 50 could be spaced away from the head 16.

The shank 20 extends lengthwise along a shank axis 26 and has a length L.

The second threaded formation 42 extends for a second length L2 along the shank axis 26. In one example, the second length L2 could be greater than 3.2mm, and could desirably be greater than 6.2mm. In one example, the second length L2 could be less than 13.2mm and could desirably be less than 10.2mm.

The transition threaded formation 82 extends for a transition length L4 along the shank axis 26. In one example, the transition length L4 could be at least 1.5 times the first pitch dimension, and could be no more than 2.5 times the first pitch dimension. In one example, the transition length L4 is substantially 2 times the first pitch dimension.

The fastener 10 includes an indication dimension 60, which is the dimension between the start of the second threaded formation 42 and the head 16.

The drill part 22 includes a drill point 90 and a drill shank 92. The drill shank 92 extends from the drill point 90 to the first threaded part 30.

The building panel 12 could be any one from the group containing insulated building panels, cladding panels, wall panels; composite building panels, cladding panels and wall panels; and so-called sandwich panels.

The building panel 12 comprises two relatively thin sheet-like skin layers 62, with a layer of insulation 64 therebetween. In one example, the skin layers 62 could be formed of metal.

In the example shown, the fastener 10 comprises a screw.

In one example, the structural member 14 could comprise a roof purlin, and the fastener 10 could be a roof panel fastener.

In one example, the first threaded formation 32 could comprise a self-tapping 12 gauge thread, with 14 threads per inch; the second threaded formation 42 could comprise a self-tapping 14 gauge thread with 14 threads per inch and the third threaded formation 52 could comprise a self-tapping thread of diameter dimension greater than 14 gauge and with less than 14 threads per inch. These details are set out in metric units in Table 1. In Table 1 , the references relate to the labels shown in Fig. 1.

In use

In use, the building panel 12 with a thickness 76 is located against the structural member 14 so that an inner one 62A of the skin layers 62 is located against the structural member 14 and an outer one 62B of the skin layers 62 is directed away from the structural member 14. The structural member 14 could be a roof purlin and could be formed of section steel, for example, box section, C section or Z section. The thickness of the section could be in the range 1 12 mm, usually 1 3 mm.

Initially, a sealing arrangement 72 is located onto the shank 20 and the fastener 10 then drilled into the building panel 12, with the sealing arrangement 72 loosely located between the head 16 and the outer skin layer 62B.

In one example, the sealing arrangement 72 comprises a rigid washer 74A and a resiliently deformable washer 74B. The rigid washer 74A could be formed of a corrosion resistant metal such as zinc plated steel, galvanised steel, aluminium or stainless steel. The resiliently deformable washer 74B could be formed of a plastics material or EPDM/neoprene.

During installation, the fastener 10 is drilled through the building panel 12 into the structural member 14. The drill part 22 drills a hole 66 through the building panel 12 and then drills a hole 68 in the structural member 14. The first threaded formation 32 self-taps a first thread in the hole 68 in the structural member 14 and threadably engages the structural member 14 to fix the fastener 10 to the structural member 14.

As the fastener 10 continues to be driven into the structural member, the third threaded formation 52 drills and self-taps a hole 70 with a third thread in the outer skin layer 62B of the building panel 12 and thus threadably engages the building panel 12.

In a correctly installed condition, the resiliently deformable washer 74B is slightly compressed by the head 16 to form a seal around the hole 70 in the outer skin layer 62B, but the force applied to the sealing arrangement 72 by the head 16 is not sufficient to cause deformation of the outer skin layer 62B or stripping of the third thread.

As the fastener 10 continues to be driven further into the structural member 14 and the head 16 starts to compress the sealing arrangement 72, the transition threaded formation 82 and then the second threaded formation 42 enter the structural member 14 and the second threaded formation 42 self-taps a second thread in the structural member hole 68.

The second major diameter dimension D2 of the second threaded formation 42 is larger than the first major diameter dimension D1 of the first threaded formation 32, but the second pitch dimension P2 is substantially the same as the first pitch dimension P1. The feature of the pitch dimensions P1 , P2 being substantially the same provides the advantage that as the second threaded formation 42 begins to screw into the structural member hole 68 the fastener 10 does not abruptly stop because of jamming or cross threading. The transition threaded formation 82 also helps reduce jamming.

The larger second major diameter dimension D2 provides the advantage that more force is now required to drive the fastener 10 into the structural member 14.

In the example shown, the second crest angle 48 is substantially the same as the first crest angle 38. The applicant has found that this arrangement reduces the risk of damage to the second threaded formation 42 (as might be the case if the crest angle 48 was smaller) while not unduly increasing the additional force required to drive the fastener 10 into the structural member 14 (as might be the case if the crest angle 48 was larger).

The explanation as to why the larger second major diameter dimension D2 requires more force to drive the fastener 10 into the structural member 14 is as follows.

The driving of the fastener 10 into the structural member 14 includes a plurality of stages as different parts of the fastener 10 drill or screw into or through the structural member 14.

1. In a drilling stage, only the drill part 22 has entered the structural member 14. The drill part 22 is driven into the structural member 14 and the drill point 90 forms the structural member hole 68. The force required is to enable the drill point 90 to drill the structural member hole 68 and is relatively high.

2. In a drill driving stage, the drill point 90 has passed through and out of the structural member hole 68 and only the drill shank 92 is in the structural member hole 68. The force required is to push the drill shank 92 through the structural member hole 68 and is relatively low.

3. In a first threaded part tapping stage, the first threaded part 30 taps the first thread in the structural member hole 68. The force now required is to enable the first threaded formation 32 to tap the first thread in the structural member hole 68 and is relatively high.

4. In a first threaded part screwing stage, the first threaded part 30 screws along the first thread of the structural member hole 68 and the force required is relatively low. 5. In a transition stage, the transition threaded formation 82 increases in major diameter dimension from the first major diameter dimension D1 to the second major diameter dimension D2, requiring a gradually increasing force to drive the fastener 10 into the structural member 14.

6. In a second threaded part tapping stage, the second threaded part 40 taps the second thread in the structural member hole 68. The force now required is to enable the second threaded formation 42 to tap the second thread in the structural member hole 68 and is relatively high.

As the fastener 10 transitions from one stage to another, the force required to drive the fastener 10 changes. In particular, as the fastener 10 transitions from the first threaded part screwing stage to the second threaded part tapping stage, the change in the force required to drive the fastener 10 will be felt and/or heard by the user driving the fastener 10. For example, if the user is using a manually driven tool such as a spanner, wrench, or the like, he/she will feel a greater resistance to driving the fastener 10 in the second threaded part tapping stage and thus be informed that the fastener 10 has reached the predetermined depth of penetration in the structural member 14. In this case the indication provided is a tactile indication.

If the user is using a powered tool such as an air or electrically powered screw gun, driver, drill, spanner, wrench or the like, the speed of the tool will drop as the tool encounters the greater resistance in the second threaded part tapping stage, which will be both felt and heard by the user as the tool speed changes. In this case the indication provided is both tactile and audible.

Thus, in the example shown, the increase in the major diameter dimension from the first threaded formation 32 to the second threaded formation 42 causes a change in the force required to screw in the fastener 10 and thus provides the indication to the user that the fastener 10 has reached the predetermined depth of penetration in the structural member 14.

The Applicant has found that the transition threaded formation 82 is important to prevent jamming of the fastener 10.

In the fixing of the building panel 12 to the structural member 14 it is important that the following criteria are met: a) the fastener 10 reaches an acceptable depth of penetration in the structural member

14 and

b) the fastener 10 is not over-driven. With regard to the first criterion, the length of the shank 20 between the start of the second threaded part 40 and the tip 18 is arranged to provide an acceptable depth of penetration in the structural member 14. Thus, when the user senses the indication provided by the second threaded formation 42 as described above, this criterion has been met. The indication provided by the second threaded formation 42 thus provides the user with the assurance that the fastener 10 has reached an acceptable depth of penetration in the structural member 14.

Wth regard to the second criterion, the indication dimension 60 is arranged to correspond with the building panel thickness 76 so that the second threaded formation 42 begins to screw into the structural member hole 68 at the same time as the head 16 begins to compress the sealing arrangement 72.

In one example, the indication dimension 60 is arranged to be at least as long as the building panel thickness 76 and desirably is greater than the building panel thickness 76.

The applicant has found that it is desirable to include an allowance dimension 78 when calculating the size of the indication dimension 60 relative to the building panel thickness 76. The allowance dimension 78 is an axial length of penetration of the second threaded formation 42 into the structural member 14 in a design installed condition, which equates to an ideal installation condition in the real world, in which, for example, the building panel thickness 76 conforms correctly to design specification and there is no gap between the building panel 12 and the structural member 14.

The indication dimension 60 is calculated as follows:

Indication dimension 60 = sealing arrangement thickness 80

+ building panel thickness 76

+ allowance dimension 78. (Equation 1)

In one example, the allowance dimension 78 could allow no less than one turn of the second threaded formation 42 in the structural member hole 68, and desirably could allow no less than 1.5 turns. In one example, the allowance dimension 78 could allow no more than three turns of the second threaded formation 42 in the structural member hole 68, and desirably could allow no more than 2.5 turns.

The applicant has found that a suitable amount for the allowance dimension 78 is to allow two turns of the fastener 10 after the second threaded formation 42 begins to screw into the structural member hole 68 and before the head 16 begins to compress the sealing arrangement 72.

In the example of Table 1 , two turns of the second threaded formation 42 at the second pitch dimension P2 (= 1.8 mm) is substantially 3.6 mm.

Thus in Equation 1 :

The sealing arrangement thickness 80 is 4 mm

The building panel thickness 76 is 78 mm.

The allowance dimension 78 is 3.6 mm

Thus, in this example, the indication dimension 60 is 85.6 mm.

The applicant has found that the indication dimension 60 will change for different thicknesses of the building panel 12 and to a lesser extent of the sealing arrangement 72. Also, a different size of allowance dimension 78 could be chosen.

The indication provided by the change of thread from the first threaded formation 32 to the second threaded formation 42 alerts the user that the head 16 is very close to compressing the outer skin layer 62B and that more attention must be paid. Also, the greater force required slows the speed of the tool as the tool approaches the correctly installed condition, enabling more attention and care to be paid in the final critical stages of the installation.

Conventional self-drilling building panel fasteners provide the operator with no indication that the fastener 10 has reached an acceptable depth of penetration in the structural member 14 and it is left to the operator to judge this by observing the tightening of the head 16 on the sealing arrangement 72. Correct installation is thus dependent on the training, skill, experience, care and motivation of the operator, but also on the actual installation details matching design specification details. The fastener of the present invention provides the operative with an indication that the fastener 10 has reached an acceptable depth of penetration in the structural member 14.

Advantageously, the second threaded formation 42 extends for a length L2 along the shaft axis 26 which caters for variations such as in the thickness of the building panel 12, bowing of the structural member 14 and the like.

Thus, in one example, the structural member 14 has bowed away from the building panel 12, effectively making the building panel 12 seem thicker than expected. In this example, the head 16 is closer to the outer skin layer 62B in fewer turns of the fastener 10 than normal. This illustrates the usefulness of the allowance dimension 78, in that the indication provided by the second threaded formation 42 still operates as long as the amount of bowing along the shank axis 26 is less than the allowance dimension 78.

In another example, the building panel thickness 76 being installed is less than that designed for. In this case, it will be necessary for the fastener 10 to be screwed further into the structural member 14, so that more of the second threaded formation 42 is located in the structural member hole 68. This is catered for by the length L2 of the second threaded formation 42 along the shank axis 26.

On receiving the indication, the user then completes the installation by screwing the fastener 10 in until the head 16 contacts and compresses the sealing arrangement 72, but stops before the outer skin layer 62B is deformed. The fastener 10 provides a tactile and/or audible indication to the user that a predetermined depth of penetration of the fastener into the structural member has been reached and alerts the user that care is required in the final tightening of the fastener against the building panel. The indication thus helps prevent over-driving of the fastener 10.

In considering the driving the fastener 10 through the building panel 12 into the structural member 14, it should be noted that the inner skin 62A is formed of a relatively thin metal compared to the structural member 14. The Applicant has found that this skin has little effect on the ability of the user to detect the indication. Any false indication caused as the second threaded part 40 begins to tap the inner skin 62A is very close to and on the failsafe side of the indication provided as the second threaded part 40 begins to tap the structural member hole 68. Other Modifications

Various other modifications could be made without departing from the scope of the invention. The fastener could be of any suitable size and shape, and could be formed of any suitable material (within the scope of the specific definitions herein).

The specifications of the first, transition, second and third threaded formations could be different to those shown and described.

In one example, the second threaded part 40 could abut the first threaded part 30, without a transition threaded part 28 therebetween. However, the Applicant has found that, in use, this arrangement has a tendency to jam.

In another example, the indicator threaded part 100 could comprise only the transition threaded part 28. In this example, the indication dimension 60 could be the dimension between the end of the transition threaded formation and the head. However, the Applicant has found that the arrangement of this example is less satisfactory than one having a second threaded part as it permits no allowance dimension.

In the example in which the pitch dimension varies between the first and second threaded formations, the transition length could be based on the average pitch dimension of the first and second threaded formations.

There is thus provided a self-drilling building panel fastener for fastening an insulated building panel to a structural member with a number of advantages over conventional arrangements. In particular the fastener provides a tactile and/or audible indication to the user that a predetermined depth of penetration of the fastener into the structural member has been reached and alerts the user that care is required in the final tightening of the fastener against the building panel.