This RRA match AR-15 trigger kit is designed to be used with Mil-Spec lower receivers with .154” trigger and hammer pins and can also be used with anti-rotation pins for a more secure fit. However, the larger .1555" pins will give you a more snug fit. The versatility of AR-15’s is extended even further as some parts are interchangeable with AR-308 and DPMS LR 308 style rifles and this trigger is compatible with both. Another accurizing feature is the lightened hammer which allows for a decreased lock time while still maintaining reliable primer ignition even with hard military surplus ammo. This fire control group provides a custom tuned feel at an affordable price whether you are upgrading an old trigger or building a new rifle.