The MBUS (Magpul Back-Up Sight) is a low-cost, color injection molded, folding back-up sight. The dual aperture MBUS Rear Sight is adjustable for windage and fits most 1913 Picatinny rail . Clamps to MIL-STD-1913 Picatinny/STANAG 4694 receiver rail and provides the same height-over-bore as standard A2 irons. Protective wings shield the dual, same plane flip apertures. Sight can still be folded with either large or small aperture in position. Detent knob easily and positively adjusts windage. Weight, with hardware: 1.3 ounces. Height above rail, stowed: ~0.51 inch. Center of aperture to top of rail: 1.42 inch. Length, stowed: 2.6 inch. Length, deployed: 1.5 inch. Windage Adjustment: ~0.7 MOA (0.754 inch/100 meter) per click with a 14.5 inch sight radius; ~0.5 MOA (0.547 inch/100 meter) per click with a 20 inch sight radius. Made in U.S.A.