Fastener

1. A fastener locking two or more sheet sections together comprising:

a shaft tapered at one end and having a driving head at another end;

a section of coarse threads running from the tapered end of the shaft towards the driving head, the coarse threads having a pitch that is greater than a thickness of a sheet section so that the section of coarse threads can quickly pass through the sheet sections;

a section of fine threads that extends from the section of coarse threads to the driving head including an uppermost fine thread adjacent the driving head, the fine threads having a pitch which is adapted to be substantially equal to the thickness of at least one of the sheet sections so that when the section of fine threads has passed through the two sheet sections, the two sheet sections remain tightly secured between the driving head and the uppermost fine threads;

wherein the section of coarse threads and the section of fine threads form a substantially continuous thread along the full length of the shaft to the driving head and a major diameter of the section of fine threads is greater than a major diameter of the section of coarse threads throughout the length of the shaft;

wherein the gauge of the fine threads is greater than the gauge of the coarse threads;

wherein the diameter of the shaft under the fine threads is greater than the diameter of the shaft under the coarse threads; and

wherein the pitch of the coarse threads is at least three times greater than the pitch of the fine threads.

2. The fastener of claim 1 wherein the tapered end is adapted to form a self-drilling screw.

3. The fastener of claim 1 in which the driving head is used to turn the screw and is any suitable head such as a recessed cross-slot head, a hexagonal head or any security or anti-tamper type screw head.

4. The fastener of claim 1 further comprising serrations disposed on an underside of the driving head adjacent to the uppermost fine threads.

5. The fastener of claim 4 wherein the serrations are angled to inhibit unscrewing movement of the screw.

6. The fastener of claim 1 , wherein the section of coarse threads comprises seven coarse threads.

7. The fastener of claim 1 , wherein the section of fine threads comprises seven fine threads.

8. The fastener of claim 1 , wherein the pitch of the coarse threads is four times greater than the pitch of the fine threads.

9. The fastener of claim 1 , wherein the pitch of the coarse threads is five times greater than the pitch of the fine threads.

10. In combination, two or more sheet sections and a fastener locking the two or more sheet sections together the fastener comprising:

a shaft tapered at one end and having a driving head at another end with a section of coarse threads running from the tapered end towards the driving head and a section of fine threads between the section of coarse threads and the driving head;

wherein the section of coarse threads and the section of fine threads form a substantially continuous thread along the full length of the shaft to the driving head;

wherein the section of fine threads have a pitch which is approximately equal to the thickness of at least one of the two or more sheet sections and includes uppermost fine threads adjacent the driving head; and

wherein a major diameter of the section of fine threads is greater than a major diameter of the section of coarse threads throughout the length of the shaft such that, when the fastener is fully inserted through the two or more sheet sections, the two or more sheet sections are tightly secured between the driving head and the uppermost fine threads.

11. The fastener of claim 10 , wherein the two sheet sections are cladding sheets.

12. The fastener of claim 10 , wherein the two sheet sections are steel purlins.

13. The combination of claim 10 wherein the diameter of the shaft under the fine thread is greater than the diameter of the shaft under the coarse thread.