Heavy Duty Xtreme Rails are built for the rigors of daily use. All HDX™ series rails feature Nitride Hardened steel QD sockets to withstand daily sling carry. Features- Rail- 6000 series extruded Aluminum Milspec Type 3 Class 2 Hard Black anodizedBarrel Nut- 7075 Aluminum  Type 3 Class 2 Hard Anodized17-4PH  Cored Stainless Steel Rail mounting attachment- Patent PendingAnti rotate tabs time Rail to upper receiver2 each 4140PH Alloy steel Nitride finished  QD sling sockets inserts, 2 on each sideNo Barrel nut shims required for installationDoes not contact or apply side loads to gas tube Inner Diameter of handguard - 1.315"Machine engraved T markings (not laser marked) will show up after paint.Includes barrel nut wrenchBarrel Nut diameter- 1.378"Compatible with most known low profile gas blocksOverall rail dimensions1.96" wide x 2.195" height11.7 ozs.-Total weight including mounting hardware and barrel nut.Made & Assembled in USA