Based on the SOPMOD designed bolt upgrade and rebuild package, this kit is designed to breathe new life into your bolt assembly. The bolt assembly is the heart of your AR15 rifle system and preventative maintenance used by professions ensures these systems keep running even under the harshest of conditions. This is a great spare parts kit to keep your AR15, M16, M4 running in the field. This kit includes: Extractor made to USGI specs (shot peened) Extractor pin BCMA(R) Extractor Spring (chrome silicon, heat treated & stress relieved, shot peened) 3 USGI Gas Rings Crane Ind O-Ring (Mil-Spec) Black Extractor Insert Mfg: Bravo Company