For grooving dirt oval foam tires. Aluminum Barrel is .740" with 2 bearings inside designed to be used with 402 Dremel Mandrel. Bearings are 3/16" ID. Aluminum barrel acts as a stop from allowing you to go too deep when grooving the cross grooves in your dirt oval foam tires. Cutoff wheels can be ground down or you can use different cutoff wheels to achieve different cross groove depths.