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. FEATURES: Impact resistant polymer construction provides light weight and resists operational abuse; Spring-loaded flip up sight easily activated from either side or by pressing the top; Detent and spring pressure keeps sight erect but allows for unobstructed folding under impact, etc.; 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.