The gas block with the Picatinny rail is constructed of T6 6061 hard coated black anodized aluminum. Is designed for a .750 diameter barrel and has a 2 1/2" top rail and weighs 2.5 ounces. The gas block is held into place with 2 #10-24 screws.  PRi gas block with Picatinny rail allows the shooter to place a front sight on the rail that is the same elevation as the receiver.  Bore Centerline to top of the rail is 1.218"