Troy Industries Fixed Rear BattleSights' is a permanent, rail-mounted alternative to a standard A2 sight that allows limitless mounting options on all-length rails with a serrated ramp to eliminate glare. Provides a continuous zero, unflinching durability. Fits all M4, M16, AR15, AR10 variants and other firearms that have a flat top receiver or removable carry handle. Will not work with a railed gas block that is higher or lower than the receiver. Front sight must be mounted at the same height plane as the rear sight. Railed gas blocks that are lower than receiver height will not zero properly.