Fastener

摘要

The fastener (10) has a head (40) and a shank (20) with a generally cylindrical section, which has a primary thread (100) of axially spaced threads of a generally uniform dimension extending the length of the cylindrical section and along the tapered tip of the shank. The fastener has a secondary thread situated between some of the threads defined by the primary thread which originates at a point in the central portion of the cylindrical section and extending upwards to terminate in a region adjacent to the head. The secondary thread has a radial dimension tapering outwards and increasing over a major portion of its length so that it is approximately equal to that of the primary thread in the region adjoining the head.