The BCM extractor spring is specifically designed for AR-15, M4 and M16 short-barreled rifles, providing a robust solution for enhanced extractor tension. Its heavy coil design not only serves specialized firearms but also significantly improves the reliability of standard 16 inches and 14.5 inches carbines. Crafted in a State-of-the-art ISO 9001 - 2000 certified facility, this extractor spring is made using cutting-edge precision equipment, upholding the BCM tradition of excellence. The product is made from premium chrome silicon material, which undergoes meticulous heat treatment to relieve stress and shot peening to enhance its strength, ensuring durability and resilience under rigorous use. The kit includes an innovative black extractor insert, a standard feature in M4, M4A1, Mk18 carbines and the latest M16A4 rifles, ensuring compatibility and enhanced performance. The BCM extractor spring is so robust that the mil-spec crane O-ring, typically used to augment extractor tension, is often unnecessary. However, for those who prefer additional assurance, the O-ring is included in the package. Choose the BCM extractor spring for unparalleled reliability and performance in your firearm. The kit comprises the following components - three BCM extractor springs made from chrome silicon, which are heat-treated, stress relieved and shot-peened; three CRANE O-rings that meet military specifications; and three black extractor inserts