The BCM extractor spring is designed for AR-15, M4 and M16 short-barreled rifles, providing enhanced extractor tension. Its heavy coil design improves reliability in both specialized firearms and standard 16 inches and 14.5 inches carbines. Manufactured in an ISO 9001 - 2000 certified facility, it uses premium chrome silicon material, heat treated and shot-peened for durability. The kit includes a black extractor insert, compatible with M4, M4A1, Mk18 carbines and M16A4 rifles. The robust design often eliminates the need for the mil-spec crane O-ring, though it is included for additional assurance. Choose the BCM extractor spring for superior reliability and performance. The kit comprises a BCM extractor spring, which is made from chrome silicon, heat-treated, stress relieved and shot-peened It also includes a CRANE O-ring that meets military specifications, as well as a black extractor insert