The PM200 M16 / AR-15 Flip Up Ranging Rear Right has all of the same great features as the standard PM136 sight. This low profile 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. In addition it is also a ranging sight. The unique rotating disc has (5) .070 diameter apertures preset to specified distances, 0=25 and 200yds 3=300yds 4=400yds 5=500yds 6=600yds. A window facing the shooter, as can be seen in the above photograph, provides a numerical indication as to the range. The sight is preset using the ballistic calculations for (55) grain through (62) grain ammunition used in the AR15/M16 16" carbine length weapon. One click allows 0.55 MOA (minute of angle) change on rifles and 0.65 MOA change on carbines. Constructed of both, black phosphated steel alloy and type III black anodized T6 aircraft grade aluminum. The sight is precision machined to fit AR-15 / M16 flat top A3 upper receiver rifles and carbines. The 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.