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 sight Dual aperture Attaches to any 1913 picatinny rail Perfect (M4) co-witness height Stainless steel clamp