The diameter of most “lightweight” profile AR-15 barrels at the gas block is .625″. There was a time when it was difficult to find low profile gas blocks to fit these narrower barrels but now there are several options including the PXT Super Light Low-profile Steel Gas Block .625″ from Parallax Tactical.
The PXT Super Light Low-profile Steel Gas Blocks are made from 4140 steel with a Melonite QPC finish. They are called “super light” because the sides are skeletonized to reduce weight.They attach via two set screws that come up from the bottom of the block.
It just makes good sense to use a lightweight gas block with your lightweight barrel. Check out the PXT Super Light Low-profile Steel Gas Block .625″.