A .625″ gas block diameter refers to the size of the barrel journal where the gas block is installed, most commonly found on light weight or pencil-profile AR-15 barrels. This gas block is designed to regulate gas flow for reliable cycling and works with .625″ diameter barrels, compatible gas tubes, and upper receiver components. It’s ideal for builders seeking a lighter rifle setup or restoring vintage AR-15 models with thinner barrels.
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