KNS Precision Non-Rotating Hammer and Trigger pins help protect your AR-15 or M16 lower receiver from damage rotating pins can cause to the lower receiver. The pins are designed not to rotate and they will not creep out of the receiver. The 0.154" diameter pins is for use with Standard Small Pin AR-15 receivers that are new or do not have enlarged hammer and trigger pin holes. For AR-15 receivers with enlarged hammer and trigger pin holes use the 0.1555" diameter pins. Mod2 pins are the STRONGEST pins produced and were designed to withstand the high impact of full and semi-automatic fire.