ProMag AR-15/M16 Single Plane Dual Aperture Flip-Up Rear Sight, Black Rear sight attaches to AR-15 / M16 flat top A3 upper receivers May be used as a back-up rear sight or a lightweight rear sight to co-witness with red dot or holographic sights Windage is adjusted using a standard A2 windage adjustment drum. The sight has both 0.199 inch and 0.73 inch apertures on the same sighting plane Constructed of both black oxide carbon steel and black anodized aircraft grade aluminum