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. A must for dead-on accuracy! Impact-resistant polymer construction resists operational abuse Spring-loaded flip-up sight is easily activated from either side or by pressing the top Spring pressure keeps sight erect but allows for unobstructed folding under impact, etc. Clamps to MIL-STD-1913 Picatinny/STANAG 4694 receiver rail Provides the same height-over-bore as standard A2 iron sights Protective wings shield the dual, same plane flip apertures Sight can still be folded with either large or small aperture in position Knob easily and positively adjusts windage Eyeball the precision by ordering today!