For many years gunmakers have been polishing barrels using a barrel spinner made from cast aluminum. These work great, but with commercial use the brittle castings are prone to cracking. These cassettes are 100% CNC machined from billet 6061 T6 bar stock. They are ergonomically profiled with radiuses on all contact surfaces to mitigate user fatigue. They fit standard 1” rectangular aluminum or steel tubing. Delrin center fitted with an O-ring in a groove that prevents the center from falling out of the inner bearing race, yet allows for easy removal. They also have a longer service life due to added material on the taper side, allowing for resurfacing of the taper.