Precision Reflex Gas Block w/ Picatinny Rail .625 Black. The rail is constructed of lightweight hard coat black anodized aluminum. The gas block weighs 2.5 ounces. The gas block fits over a .625 diameter barrel. Block locks into place with 2 crossbolts the same as our original gas block front sight. Specifications for Precision Reflex Gas Block w/ Picatinny Rail: Manufacturer: Precision Reflex Color: Black Fabric/Material: Aluminum Gas Block Journal Size-Diameter: .625 in Gun Make: AR Platform Package Contents: Precision Reflex Gas Block w/ Picatinny Rail Precision Reflex 05-625-04: Gas Block w/ Picatinny Rail .625 Black