Self-drilling and self-threading screws.

摘要

A drill screw for drilling through soft packing material such as timber into a steel purlin has a drill point (12), a threaded shank (11) and a head (13). The srew thread (14) is interrupted by longitudinally extending flutes (19) otherwise adapted to become at least partially filled by loose packing material generated by drilling so that the thread tends to ream out the packing material and prevent an effective threaded connection between packing material and drill srew. This allows the drill screw to advance at the normally required slow advance when the drill point engages the purlin.