Primary Arms sent this to me in my email today. With P A you get the price at check out. This is a new idea to tighten/loosen the barrel nut when assembling a barrel to an AR upper. Looks to me like a better idea for barrel attachment. 1- Clamp the fixture in the jaws of a bench vice. 2- Attach the upper receiver to the fixture, and pin the receiver to the fixture through the upper receivers pivot lug. 3- Insert the barrel into the upper receiver trunnion indexing the barrel extension on the splines of the top extension of assembly fixture. 4- Remove the bolt from a BCG, then insert the bolt carrier into the upper receiver sliding the bolt bore of the carrier onto the post on the top side of the fixture. This is to add additional support to the upper receiver. 5- Tighten the barrel nut. The idea is with the barrel held in place by the barrel extension indexed on the fixture’s spline’s when tightening the barrel nut, the torque is divided between the barrel and upper receiver. This also eliminates the barrel from rotating when tightening the barrel nut and the possibly of distorting the upper receiver’s trunnion barrel index slot, and possibly shearing the barrel’s index pin.