Thread forming self-locking screw

A thread forming and vibration resistant fastener for use in a workpiece comprising a shank having at least a portion of its length provided with an external thread defined by a load bearing thread flank and a non-load bearing thread flank, a first portion of said thread having an irregular surface configuration formed on both of said flanks and a second portion of said thread having said irregular surface configuration formed on said load bearing flank only, said irregular surface configuration comprising a plurality of serrations in the form of teeth when viewed along a cylinder concentric with the longitudinal axis of said fastener, said teeth extending inwardly from adjacent the crest of said external thread portion, between the flanks thereof, to a termination inwardly of the pitch diameter thereof, each of said teeth comprising a ramp inclined relatively gently with respect to a plane parallel to the helix angle of said thread in the direction of rotation for engaging the fastener in the workpiece, said ramp extending from a root portion at the forward end of said ramp with respect to said direction of rotation to a crest portion at the rearward end of each of said teeth and a relatively steeply inclined wall defining a buttress with respect to a plane parallel to the longitudinal axis of the fastener, said buttress extending from said crest portion to the root portion of an adjacent tooth, said first thread portion further having an irregular peripheral configuration along the crest thereof, said irregular peripheral configuration comprising extension portions of each of said teeth extending radially beyond the original diameter of the unserrated thread portion crest, each of said extension portions having a maximum diameter adjacent said root portion of their associated teeth and being tapered from the maximum diameter to a minimum diameter adjacent said crest portion of their associated teeth;

• whereby an interrupted contact is provided between said crest portion of each of said teeth and the workpiece as the fastener is turned into the workpiece to produce a complementary thread therein with a minimum of drag torque, and whereby said teeth on said load-bearing flank, only, cooperate with the mating workpiece thread flanks upon the inducement of a compressive load in said fastener, substantallly elastically deforming a portion of the mating thread flanks causing a lapping over of the material of the workpiece against said buttresses to preclude back off of said fastener from an engaged, compressively loaded condition.