Patent ID: 8684646

Claim:
A thread forming fastener comprising a drive head ( 22 ) and a shank ( 24 ) extending from the drive head, said shank including a core ( 26 ) and a helical thread ( 28 ) formed on the core, said thread ( 28 ) having a tip ( 8 ), a selected thread height ( 36 ), a selected axial pitch ( 38 ) and a profile which in axial cross-section is non-symmetrical and includes a radially inner concave leading face portion ( 42 a ) with a first radius ( 41 ) and which transitions smoothly to a radially outer convex leading face portion ( 42 b ) with a second radius ( 53 ) shorter than the first radius ( 41 ) at a transition location ( 43 ) spaced a distance from said tip ( 8 ) equal to 22-27% of said selected thread height ( 36 ), a blending portion ( 46 ) at said tip with a third radius ( 63 ) shorter than said second radius ( 53 ), said blending portion having a first end which blends smoothly with said radially outer convex leading face portion ( 42 b ) and a second end which blends smoothly with an outer end of a convex outer portion ( 44 b ) of trailing face ( 44 ) and whose radius ( 62 ) is longer than said first radius ( 41 ), said trailing face ( 44 ) extending inward to said core ( 26 ).