Obsidian Arms Enhanced AR-15 Bolt Carrier Pin Kit Steel. Specifications for Obsidian Arms Enhanced AR-15 Bolt Carrier Pin Kit: Manufacturer: Obsidian Arms Color: Stainless Steel Finish: Nickel Fabric/Material: 4340 Alloy Steel Caliber: Universal Gun Make: AR Platform Gun Model: AR-15 Gun Type: Rifle Hand: Ambidextrous Country of Origin: USA Features of Obsidian Arms AR-15 5.56 Enhanced Bolt Carrier Pin Kit Made from 4340 alloy steel for strength. Heat treated for durability. Hard Chromed for additional durability corrosion resistance and minimal surface friction. Package Contents: Obsidian Arms AR-15 5.56 Enhanced Bolt Carrier Pin Kit What firearm models does the manufacturer say Obsidian Arms Enhanced AR-15 Bolt Carrier Pin Kit is compatible with? The manufacturer says that Obsidian Arms Enhanced AR-15 Bolt Carrier Pin Kit is compatible with AR-15Obsidian Arms OA-AR-15-BCPK: Enhanced AR-15 Bolt Carrier Pin Kit Steel