Self tapping screw for sheet metals - has pyramid type point piercing sheet and forming lip prior to tapping

摘要

The self tapping screw is of the conventional type but its point has the form of a four-sided pyramid. For the first portion (15) (approx. 1/3) of the point the sides meet to give sharp edges (16) but along the remainder 17, this edge is removed by an increasing radius (18). A hole is formed by pressing the screw through the sheet (19), the angled faces forming the metal into a lip (21) to give an extended thread length. The thread is formed, conventionally, by rotating the screw clockwise with a downward pressure.