Screw fastener blank

摘要

A bi-metallic screw fastener blank for a self drilling screw of a given root diameter is disclosed. The screw blank comprises a metallic head and shank member made of a first material that is welded to a metallic slug member that is of equal diameter to the head and shank member but is made of a second material which is heat hardenable. The blank is characterized by an annular groove at the weld interface between the head and shank member and the slug member that has a diameter equal to the given root diameter of the screw.