The low profile gas block for .625 diameter barrel is constructed of 303 Stainless Steel with a nitrite finish. The gas block is held in place by 2 10-32 set screws. The gas block is 1.3" tall 1" in length and is .625" from bore center to gas tube. 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.