US Patent 9046121 Screw with dual edge on thread

A screw fastener having a head, threaded shank with compound, divided threads and tip end has an upper thread surface extending at a substantially flat angle from a normal to a longitudinal axis 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.