The Troy Industries Flip-Up Rear Battle Sight is a locking sight designed for flat top receivers. The sight is made of hardened T6 aircraft aluminum with stainless steel components. The sight features two apertures, attaches to the rail with a flathead cross-bolt. The DOA aperture is optically engineered to center your eye faster, and provide a more clear target picture than standard round apertures. Dual apertures with a 0-300 meter setting and a 500 meter setting. Rear sight aperture includes tritium light inserts. Notes: The measurement to the center of the standard aperture is 1.36". The standard sights are meant for Mil-spec top rails. FeaturesFixed Rear SightDual DOA AperturesTritium in 0-300m ApertureCross-bolt Mounting