Doublestar Corp. Bolt Carrier Rebuild Kit, Contains 1 Extractor, 1 Extractor Spring With Bumer Pad, 1 Set of 3 Gas Rings, 1 O Ring, 1 Extractor Pin, 1 Firing Pin, 1 Firing Pin Retaining Pin, 1 Gas Key, 2 Gas Key Screws AR789 High quality components and precise manufacturing make ACE parts ideal for maintaining and upgrading firearms. The durability" reliability and excellent build quality of these parts will ensure years of service you can count on.