SCREW WITH DUAL EDGE ON THREAD

摘要

A screw fastener (1) having a head (H), threaded shank (S) with compound, divided threads (T) and tip end (P) has an upper thread surface extending at a substantially flat angle from a normal to a longitudinal axis (3) of the screw which diverts upwardly to a first peripheral edge defining a cupped or concave upper thread surface and a lower thread surface extending upwardly to a second peripheral edge, with a radially inward recess between first and second edges. The screw exhibits significantly increased pull-out resistance.