Advanced design, superior sighting and battle-ready toughness define Troy Industriesí new Di-Optic Aperture (DOA) flip-type sights. Now available with Tritium, a form of hydrogen that emits its own light source, ideal for any low-light shooting situation. These sights provide lightning fast target acquisition and are manufactured to exceed military specs. The optically engineered apertures center your eyes instantly and effortlessly providing a clearer target picture than with round apertures. The sights feature two settings, one for up to 300 meters and a second for up to 550 meters. This versatility makes the DOA ideal for military, law enforcement and home defense applications. These advanced sights have been extensively field-tested and, like all Troy Industries products, are Battle Ready. Count on it. - Flat Dark Earth Note: Sight is designed to work on same plane rail systems only. Will not work with a railed gasblock that is higher or lower than the receiver.