METRIC FAL , ....US MFG. HAMMER ...and have the smaller diameter trigger pin hole ......unlike the l1a1 hammer which have a slightly larger pin hole diameter.....................................................................................................................................COUNTS AS ONE (1) US 922 COMPLIANT PART....VERY WELL MADE .... IDENTIFIED BY THE LETTER "C" IN A CIRCLE ............................................................................................................................................THESE WERE MANUFACTURED BY "THOMPSON INVESTMENT CASTING" OF ROCHESTER , NEW HAMPSHIRE......WHICH WAS LOCATED ON THE SAME PROPERTY OF THOMPSON CENTER ARMS.... OWNED AND OPERATED BY ONE OF THE OWNERS OF TC..... THEY MANUFACTURED... ALL OF THE THOMPSON CENTER SMALL PARTS HAMMERS ,SEARS ,TRIGGERS , SIGHTS ETC. FOR ALL OF THOMPSON CENTER ARMS PRODUCTS....NOTE: SEVERAL HAMMERS WERE USED IN THE PHOTOGRAPH ....TO LET YOU SEE ALL SIDES OF THE ITEM....AD IS FOR ONE (1) HAMMER.....