Improvements relating to self-drilling screws

摘要

A self-drilling screw fastener (40) has a shank (42) with a drive head at one end and a penetrating portion at the other end, the portion ending at a sharp tip (50). A single-start screw thread (52) runs from the tip (50) towards the head. The thread (52) comprises a helical ridge rising from a core portion of the shank (42). At the penetrating portion of the screw fastener (40), there is an elongate indentation (48) having a total length in the range of 1.0 to 3.0 times the pitch (P) of the thread (52), a maximum width in the range of 18 % to 55 % of the diameter of the shank (42), and one end substantially at the tip (50). The preferred method of manufacture is to roll form the thread (52) and the indentation (48) in a single pass of a roll-forming die