Advanced design, superior sighting and battle-ready toughness define Troy Industries new Di-Optic Aperture (DOA) fixed sights.Looking for rock solid stability and dead-on accuracy in a fixed sight? Troy Industries Di-Optic Aperture (DOA) fixed sights get the job done with an advanced design, superior sighting ability and battle-ready toughness.. This permanent, rail-mounted alternative to a standard A2 sight allows limitless mounting options on all-length rails with a serrated ramp to eliminate glare. Provides a continuous zero, unflinching durability and peace of mind. These sights provide lightning fast target acquisition and are manufactured to exceed military specs. The optically engineered Di-optic 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.Specifications:- Note: Sight is designed to work on same plane rail systems only. Will not work with a railed gas block that is higher or lower than the receiver.- Di-Optic Apertures improve sight acquisition speed - Increases accuracy out to 550m - Exclusive Battle Ready design - Installs and adjusts easily - Aircraft aluminum 6061 & stainless steel - Type III hard coat w/ black oxide or Flat Dark Earth finish - Hardened T6 aircraft aluminum construction with stainless steel components - Fits all M4, M16, AR15, AR10 variants and other firearms that have a flat top receiver or removable carry handle. - A permanent rail mounted alternative to a standard A2 rear sight or carry handle - Provides constant access to fixed sights that continuously hold their zero - Extremely durable and reliable providing peace of mind - The most rugged fixed rear sight available