These are the Generation 2 Mod 2 pin sets by KNS Precision INC. They are the STRONGEST pins that can be produced and were designed to withstand the high impact of full and semi-automatic 9mm and .223 suppressed weapons. They will also fit the .308 AR rifles. The pins are black nitrided stainless steel. End retainers are Dark Earth. An absolute must-have for all M-16 owners. They will also protect your AR-15. Special anti-creep retainers prevent wear on your irreplaceable M-16 or AR-15 receiver. Pin installation tool & 2 TORX wrenches & screws included. No modification to firearm required. The .1555 dia. pin is for worn receiver trigger and hammer pin holes. Being non-rotational, further wear is eliminated. They will also fit new receivers and will remove the free-play in match triggers.