This multi-use tool helps with ease of installation of barrel nuts without scratching the exterior. Also a great way to securely hold your AR's upper receiver assembly for maintenance and upgrades. Now with newly added Torque Block, for those really extra heavy duty jobs. These tools are made to grip in a bench vise so that the rod is either vertical or horizontal. You then slide the upper receiver onto the reaction bar. The splines on the front of the rod enter the into barrel extension for a secure hold and fit. Ready for tuning, it's that simple. Can handle over 90 ft/lbs of torque.