ProMag AR15/M16 Flp Up.Rr.Sngl Pln Apert This rear sight attaches to AR-15 / M16 flat top A3 upper receivers. The sight may be used as a back-up rear sight or a lightweight rear sight to co-witness with red dot or holographic sights. The sight locks in its upright position, a spring loaded release must be depressed to place the sight in the down position. The sight has both 0.199 inch and 0.73 inch apertures on the same sighting plane. This allows both apertures to be sighted to the same point of impact. The sight has four apertures so that rotating the dial in either direction brings the next size aperture to view. The windage is adjusted using a standard A2 windage adjustment drum. One click allows 0.55 moa change on rifles and 0.65 moa change on carbines. Constructed of both black oxide carbon steel and black anodized aircraft grade aluminum.