The low profile gas block for .625 diameter barrel is constructed of 1141 high strength steel with a Nitrite finish. This gas block is held in place by 2 10-32 set screws. Gas block is 1.3" tall 1" in length and is .625" from bore center to gas tube. The block is .775 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.