Tacfire's a2 mil-spec buffer tube kit is a replacement to a damaged stock system or to transition from a 6 position stock this kit allows the acceptance of a standard a2 stock to me installed.A2 stock not included.For 5.56/.223 ar-15's only.Length of spring 12.75".Rails: BlackType: Buffer AssemblyFirearm Type: A2 Mil-SpecFirearm Model: 6' LMaterial: 223 Remington/5.56 NATOFinish: Aluminum