This is a Magpul Industries Sight known as the MBUS, model MAG248-GRY.
The MBUS (Magpul(R) 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:
Polymer construction
Spring-loaded flip up sight
Protective wings shield the dual same plane flip apertures
Easily adjust Windage
