Durability and dead-on accuracy make Troy BattleSights the hands-down first choice of Special Ops and Tactical Users Worldwide. Troy's HK Front Fixed BattleSight, a permanent, rail-mounted alternative to a standard A2 sight, allows limitless mounting options on all-length rails with a serrated ramp. Features snag-free apertures at factory height. 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. 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. Requires front sight tool. Standard M16 A2 front sight.