The sxt series handguards feature a free-floating ar-15 handguard with an m-lok attachment system.The simple clamping system uses two cross bolts which fit into the barrel nut for a rapid and easy installation.(the old sxs series clamping system used a bias block on the bottom to secure the forearm to the barrel nut which required knurling).Inside diameter 1.25", outside diameterFirearm Type: AR-PlatformMaterial: 6061-T6 AluminumFinish: Black AnodizedFree Floating: Yes