The Samson Evolution Series free-floating AR-15 rail offer the perfect upgrade for 3 gun shooters, LE/Military or weekend enthusiasts. Evolution rails provide a continuous Mil-Spec top rail, dual anti-rotation tabs and they are relieved for most gas piston systems. The 1.8" faceted outside diameter offers a comfortable shooting platform while not being too large for most shooters and the inside diameter is large enough to fit most suppressors (1.56").The thermal bushing help reduce heat transfer to handguard and lock onto the stock barrel nut, with no special tools required for installation. Accessory rails can be added or removed easily to adapt the handguard to your needs (units can also be mounted at 45 degree offsets). *Note: Does not include barrel nut.