6-position receiver extension tube with mil-spec diameter for rifles * Tight tolerance control for zero-gap fit with polymer stock and receiver to meet demands of silent operations * Easy to mount and no modification needed * Aircraft Aluminum with anodized finish * its ALL standard rifles Colt, Bushmaster, Del-ton, Stag, DPMS, ect...Perfect if you are swapping stock to Magpul, Vltor, ect..