KAC's line of Micro Iron Sights are currently in use by the United States Army, Marine Corps and numerous law enforcement agencies worldwide. This is because they are built to exacting tolerances, maintain their zero under adverse conditions and, when folded, have one of the lowest profile top-rail footprints in the industry. The simple and rugged 300 Meter Folding Micro Rear Sight has a fixed post aperture, which is ideal for shooters who want an easy to use, close to medium range back-up sighting solution. The 300 Meter Micro Rear Sight is adjustable for windage only, and includes a snap-in polymer aperture insert that gives the user a more precise sight picture if desi Mfg: Knights Armament SPECS: Fits - Picatinny rails. Adjustable sights are calibrated for 5.56x45mm NATO cartridge.