Thread tapping screw

Abstract

A threaded fastener is presented of the thread-forming type, wherein there is defined, during driving thereof relative to a workpiece a combination of force couples and a resultant moment of force couples to develop material flow of the workpiece material about the threads to give face contact between the mating threads of the fastener and threads formed in the workpiece thereby for improved loading. The threaded fastener comprises a threaded body portion defining an axis and a driver head portion, and including a thread profile in axial cross-section having a plurality of zones including a first zone comprising a trailing thread face with respect to the direction of advancement of the fastener into the workpiece, which trailing thread face defines a first angle relative to the axis of the body portion and a second zone comprising a radiused forward thread face which defines a predetermined radius of curvature, such that the material of the workpiece is induced to flow, during thread forming, generally radially inwardly and forwardly with respect to the direction of advancement of the fastener relative to the workpiece toward the trailing angled face for increased surface contact therewith to thereby achieve a high friction between the mating threads of the workpiece and the trailing face and to reduce the tendency for the fastener and workpiece to become loosened under externally applied forces in service, and to give an improved relation of tapping torque to stripping torque, and to reduce hoop stress in the material of the workpiece.