... ),TA1 TA2 TC4, etc.Thread typeA:Triangle thread: (60 degrees): Combination / lockB:Triangular thread: (55 degrees): Combination / lockC:Trapezoidal thread (30 or 29 ... degrees): Power TransmissionD:Square thread (90 degrees): Power TransmissionHead CodeFlate,Oval,Round,Pan,Truss,Hex,etc ...