Complete 6mm ARC Advanced Rifle Cartridge Bolt. Features a 9310 steel bolt, heat treated, hard turned and shot-peened for increased surface strength and durability, and an extractor booster to ensure reliable cycling during rapid semi-auto or full-auto fire. Parts are magnetic particle inspection tested in batches to ensure it’s free from imperfections that can lead to premature failures. Bolt has a .136 head spacing commonly referred to as the type 2 bolt. We also offer a type 1 bolt or 7.62x39 with a .125 head spacing. Please make sure you check with your barrel manufactufe to make sure you order the correct bolt for your barrel. Allways use headspace gages to check barrel and bolt is properly headspaced. Head spaced to Satern, Lilja, Precision Firearms,Proof Research Barrels, X-Caliber, Wilson Combat, and Noveske Rifleworks.