NCStar's Tri-Rail Receiver Cover provides three rails for mounting an optic on top and accessories. The two side rails can be mounted in several positions for mounting flexibility, and are also removable. Four side set screws allow the receiver cover to be locked to the receiver for a secure fit. The see-through design allows you to still use iron sights when mounted. It is constructed of steel with an aluminum rail.
Specifications:

Type	Tri-Rail
Model	Tri-Rail
Dimensions	See Thru
Size
Material	Black
Action	Aluminum/Steel
Trigger	1
Safety	Rifle
Thread Pattern	Screw (4)
Finish	4.8"
Bolt Type	No
Hand
Hammer Type
Max Capacity