Precision Reflex Low Profile Gas Block .750 Adjustable Steel Black. 750 diameter barrel is constructed of 1141 high strength steel with a magnesium Phosphate finish. Gas block #8-32 adjustment set screw. The gas block held in place by 2 10-32 set screws. The block is 1.38in tall 1in in length and is .625in from bore center to gas tube. It is .920 in width and comes with a roll pin. From the back of the gas block to the gas port hole is .250. This leaves .035 between the back of the gas block and most steps in the barrel. This is for installing of the A2 style hand guards. So there should be a .035 gap between the barrel step and the gas block. This can be filled with spacer or leave empty. Specifications for Precision Reflex Low Profile Gas Block: Manufacturer: Precision Reflex Color: Black Fabric/Material: Steel Gas Block Journal Size-Diameter: .750 in Gun Make: AR Platform Condition: New Package Contents: Precision Reflex Low Profile Gas Block Precision Reflex 05-075-03: Low Profile Gas Block .750 Adjustable Steel Black