The Ergo 4821 .750 Low Profile Gas Block is designed to fit under the Ergo Modular and SuperLite Rail System, as well as most other manufacturer's free float handguards. CNC machined 4140 chromoly steel Black Nitride/Melonite Quench Polish Quench (QPQ) finish Chamfered edge, slip on fit Weighs 2 oz Fits under most free float handguards USA made steel & Machined in the USA Internal Diameter 0.750 inches Includes (2) set screws for a secure attachment Accepts standard gas tube roll-pins (roll-pin NOT included)