Midwest Industries MI-CRM6 AR-15 Free Float Hand Guard 6" Overall Length 4140 Heat Treated Barrel Nut Barrel Nut and Wrench Included Features Patented 4140 Heat Treated Torque Plate 6061 Aluminum Type 3 Hard Coat Anodized Continuous MIL-STD 1913 Picatinny Top rail Two Integral Anti-Rotation QD Sling Sockets Super Slim 1.5" Outside and 1.3" Inside Diameter Seven Sides of M-LOK 5-Slot Polymer M-LOK rail included Fully Dehorned and Deburred 100% Made in USA Midwest Industries Lifetime Warranty Matte Black Manufacturer's Note:Due to the many different dimensions in BILLET UPPER RECEIVERS on the market, please contact your billet upper receiver manufacture to insure fit of this hand guard. This hand guard is compatible with standard forged upper receivers. NOT FOR USE ON GAS PISTON AR's!