This MBUS (Magpul back-up sight) Pro rear sight mounts to Mil-Std 1913 Picatinny rails. Positive detents keep the flip sight at standard AR sight height when deployed. Includes windage adjustment knob (no tools required). All steel construction, case hardened and finished with Melonite QPQ for extreme resistance to wear and corrosion. Weighs 1.8 ounces. MADE IN THE U.S.A.