Vibration-resistant thread-forming screw

Claim 1

A one piece vibration-resistant, thread-forming screw comprising an elongated shank having a continuous exterior thread and a plurality of exterior lobes distributed circumferentially about said shank and extending spirally therealong in an angular direction opposite from said thread, said shank having in any plane normal to its axis an inner solid core portion of circular configuration and said lobes projecting outwardly beyond said core portion, being integral therewith, and being uniformly distributed circumferentially about said axis, each lobe having in the direction in which the shank is turned when threaded into a body a relatively long leading leg and a relatively short trailing leg, said leading leg continuing to progress gradually away from said core portion in said direction of turning out to a point of maximum distance from the shank axis where it meets its associated trailing leg which returns abruptly from said point toward said axis in said direction of turning of said shank into a body, each trailing leg being concave at its innermost region where it adjoins the circular core portion and forms a junction with the leading leg of the next lobe, said threads having crests and roots both conforming to the lobular configuration with said thread having a uniform radial dimension between its crest and root throughout the extent thereof, said point of maximum distance on each lobe being located substantially in axial alignment with a junction between two other immediately axially adjacent lobes.