The Same Plane Lowe Profile Back Up rear sight is a folding low-profile rear sight that mounts on any flattop AR-15 upper receiver or picatinny rail. The sight measures only .4375" tall when folded. It locks firmly in the up or down position via a detent button, ensuring positive activation. The micro windage knob features the same MOA adjustments as a standard M16, .65 MOA on M-4 style rifles and .49 MOA on A-4 style rifles. Constructed of hard anodized 6061 aluminum.