Durability and dead-on accuracy make Troy BattleSights(TM) 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 : 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