Head drive for threaded fastener

摘要

A threaded fastener having a recess or projection in a head for engagement with a jointing equipment is disclosed. The recess or projection is composed of a center portion and radial portions extending radially outward of circumference of the center portion. Each of the radial portions includes a pair of straight line section and a rounded corner to prevent stress concentration for providing substantial strength against press-molding and applied torque.