The BCMA(R) Extractor Spring is a heavy coil design made for the increased extractor tension required on many AR15, M4, M16 short barreled rifles. This product also improves the reliability on a standard 16" and 14.5" carbines. As with all BCM branded products, the highest quality is the primary focus. Our BCM Extractor Spring is manufactured by a 9001:2000 facility employing the latest precision equipment. BCM starts with only the highest quality chrome silicon material, heat treats to stress relieve the product and shot peens to add increased strength. This kit also includes the new black extractor insert, standard on all M4, M4A1, Mk18 carbines and the recent new standard on M16A4 rifles. The BCM Extractor Spring is so strong the Mil-Spec Crane O-Ring will probably not be needed, but it is included. This kit includes: - BCM Extractor Spring (chrome silicon, heat treated & stress relieved, shot peened) - Crane Ind O-Ring (Mil-Spec) - Black Extractor Insert