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 equipped weapons, but is specifically tailored to the AR15/M16 platform. Spring-loaded flip up sight easily activated from either side or by pressing the top release. 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. 0.7 MOA (0.754"/100m) per click with a 14.5" sight radius. 0.5 MOA (0.547"/100m) per click with a 20" sight radius. Cannot be mounted to a railed gas block due to excess heat issues. Front MBUS must be mounted to a railed fore end on the same plane as the receiver rail. Because of this the sight is also not compatible with MOE Hand Guards. Made in the USA.