This is a TROY Sight known as the BattleSight, model SSIG-FBS-FHBT-03.
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
