The revolutionary, patent-pending Drivelock design in collaboration with Icon Defense, uses three independent wedges that interface with the angular grooves in our proprietary barrel nut. This system clamps the rail onto the steel barrel nut with extreme force and precision, while also driving the handguard rearward towards the upper receiver. The slightly larger ID of that extrusion gives users more real estate around the gas block, even more rigidity than the M76, and takes longer to heat. Lengths Available: 8a ^2- 13.1oz 9.5a ^2 - 14.4oz 10.5a ^2 -14.6oz 11.5a ^2 - 15.6oz 13a ^2 - 16.6oz 13.75a ^2 - 17 Mfg: Sons Of Liberty Gun Works