Barrel Vise
A heavy clamping vise that grips the barrel while the action is torqued, the partner tool to an action wrench for barrel swaps.
A barrel vise clamps the barrel along its length with enough force to keep it from rotating while torque is applied at the action end. Most use split bushings lined with rosin or a similar grippy compound so the steel can be held tightly without scarring the finish, and the whole vise is bolted to a sturdy bench to absorb the load. The grip has to be firm because the threaded barrel joint is set to a high, precise torque.
Used together with an action wrench, the barrel vise makes it possible to remove a factory barrel and install a new one without damaging either part. This pairing is what lets a competent hobbyist or smith fit a shouldered prefit barrel, a job that used to require a full lathe setup and dedicated gunsmithing experience.