Helically Coiled Inserts are precision formed from a diamond shaped wire made out of 18-8 stainless steel (type 302/304). They are work hardened to a tensile strength above 200,000 to 250,00 P.S.I. and a hardness of Rc 43-50. The finished surface (8-16 micro inches) is smooth, which eliminates friction induced thread erosion. When installed into a tapped hole, the insert provides permanent conventional screw threads. Helically Coiled Coil-Sert? Inserts are precison formed from a diamond shaped wire Screw Thread Inserts are available in Standard (Free Running ) and Screw-Lok Type.