ProMag AR-15/M16 Ranging Flip-Up Rear Sight&rlm;, Black This low profile rear sight attaches to AR-15 / M16 flat top A3 upper receivers Preset using the ballistic calculations for (55) grain through (62) grain ammunition used in the AR15/M16 16" carbine length weapon Constructed of both, black phosphate steel alloy and type III black anodized T6 aircraft grade aluminum Sight is mounted to the rail via a locking bar and secured with a cross slotted, knurled thumb screw No permanent modification required for installation; all hardware is included