These U.S.A. made Tapco G2 Double hook semi-auto trigger groups are manufactured with 4140 tool grade carbon steel, have a mil spec dark black oxide finish.  Precision secondary machining ensures perfect fit and function.  They are heat treated to 45-48C Rockwell.  Improved trigger pull (3-4 lbs), no painful trigger slap.  Standard sized trigger and hammer pin holes can still be used.  Counts towards 3 compliance parts and comes with a lifetime warranty.