Samson fixed sights are the most robust fixed combat sights on the market. Accepts all aftermarket rear aperture replacements with Mil-spec dimensions. It is not intended for lower height gas block rails. The durable construction and solid mounting system guarantees you to stay on zero.Features :Fixed rear sightDual apertureAttaches to any 1913 picatinny railPerfect (M4) co-witness heightStainless steel clamp