The Geissele AR10/SR25 Super Reaction Rod, model 10-247, is a tool designed to securely hold an upper receiver assembly for maintenance and assembly work. By gripping the Reaction Rod in a bench vise either horizontally or vertically, the upper receiver can be slid onto the rod, and the rod's integral splines enter the barrel extension to secure it from turning. This prevents damage to the aluminum receiver and ensures precise installation of barrels, flash hiders, gas blocks, and handguards. Made from 4140 Chrome Moly Steel, this rod is essential for any gunsmith or firearm enthusiast. Geissele Automatics Geissele AR10/SR25 Super Reaction Rod 10-247