This is a TROY Sight known as the BattleSight, model SSIG-FRS-R0BT-00.
"Looking for rock solid stability and dead-on accuracy in a fixed sight? Troy Industries Fixed BattleSights(TM) get the job done. This permanent" rail-mounted alternative to a standard A2 sight allows limitless mounting options on all-length rails with a serrated ramp to eliminate glare. Provides a continuous zero" unflinching durability and peace of mind. The Troy Rear Fixed Rail 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.
Features:
A permanent rail mounted alternative to a standard A2 rear sight or carry handle
Provides constant access to fixed sights that continuously hold their zero
Fits all M4 M16 AR15 AR10 variants and other firearms that have a flat top receiver or removable carry handle
