Phase 5 Weapon Systems Inc Low Profile Gas Block Set Screw Black Gas Block - Lo Pro SetScrew. It is mounted by the use of two clamping screws. Specifications for Phase 5 Weapon Systems Inc Low Profile Gas Blocks: Manufacturer: Phase 5 Weapon Systems Inc Color: Black Coating: Mag Phosphate Fabric/Material: 4140 Chromoly Steel Gas Block Journal Size-Diameter: .750 in Weight: 1.8 oz Features of Phase 5 Weapon Systems Inc Low Profile Gas Blocks Compatibility: 0.750in Barrels Material: 4140 Chromoly Steel Finish: Mag phosphate Weight: 1.8 oz. Width: 0.90in Height: 1.48in Package Contents: Phase 5 Weapon Systems Inc Low Profile Gas Blocks Phase 5 Weapon Systems Inc Gas Block - Lo Pro SetScrew: Low Profile Gas Block Set Screw Black