Threaded fastener

Claim 1

A threaded fastener comprising an elongated shank on which a helical thread form is disposed, a workpiece entering portion of said shank disposed at one end thereof and a tool accommodating head disposed at the opposite end of said shank, and having a concave thread facing surface extending radially outwardly from the centerline of said shank beyond said helical thread form, a plurality of ribs disposed on said thread facing surface of said fastener and spaced circumferentially about the centerline of said shank under said head and positioned to contact a workpiece through which said workpiece entering portion of said shank is inserted upon rotation of said helical threads in said workpiece, each of said ribs comprising a brake surface extending radially outwardly from a point adjacent to the intersection of the outer periphery of said shank and said thread facing surface and having an outer edge for contacting said workpiece and an inner edge spaced from said outer edge in a direction away from said workpiece and a ramp surface sloping from said brake surface outer edge away from said workpiece, each of said ribs culminating in a tooth-like projection located at the outer periphery of said thread facing surface and each tooth-like projection comprising a brake surface and a ramp surface facing said centerline which ramp surface of said tooth-like projection has the shape of a quartered portion of an ellipsoid; whereby rotation of said fastener in one direction causes said ramp surfaces to slide along said workpiece and rotation of said fastener in the opposite direction causes said brake surfaces to penetrate said workpiece producing a braking action.