Geissele Triggers is well known for making top-notch, quality AR-15 triggers. The Reaction Rod is machined to these same exacting standards to deliver reliable performance over years of hard use. Designed to securely hold an upper assembly for maintenance and assembly, the Reaction Rod engages the splines in the barrel extension, allowing the stress to be placed on the steel barrel extension, instead of the softer aluminum receiver. Simply clamp the rod into a bench vise in the desired position and slide the upper receiver and barrel onto the rod. This allows the user to torque down barrel nuts, install flash hiders, gas blocks and handguards with ease. This eliminates all worry about twisting or cracking the fragile upper receiver and even allows work to be performed without removing sights and optics from the receiver's top rail.