It's a good rule of thumb to have extra accessories on hand while running your tumbler. You never know when Fido is going to get hold of the tumbling belt or barrel and chew it to pieces because it tastes like dirt. So stock up on the rotary tumbler parts and accessories that you're bound to need, and be prepared.
You can learn more about rock tumbling in our "Learn and Explore!" Rock Tumbling and Polishing pages.