1555 kit fits ar's that have been shot a lot or a lower with loose pins I ordered this by mistake I need 1554. $20 cash or trade for 1554 kit or ? 503-871-0456 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. The .1555 will not fit Jewell Trigger System.