The rear 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 abuseSpring-loaded flip up sight easily activated from either side or by pressing the topDetent 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 ironsProtective wings shield the dual, same plane flip aperturesSight can still be folded with either large or small aperture in positionDetent knob easily and positively adjusts windage | Magpul GEN 2 MBUS Rear Flip Sight