This is a TROY Sight known as the BattleSight, model SSIG-FBS-FMBT-02.
Durability and dead-on accuracy make Troy BattleSights(TM) the hands-down first choice of Special Ops and Tactical Users Worldwide. Troy's M4 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 can be moved or taken off without permanent modification to the firearm
Features snag-free apertures at factory height
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
