If you're looking to build some kind of rotary processor, I found a cheap way to get ball bearings for the shafts for the wheels that support the drum. As the fidget spinner craze has died, stores are selling them off dirt cheap. I bought 8 at Ollie's for a buck each, There are 3 bearings with a 1/4 diameter hole in the center of the bearing and the center bearing from the spinner is smaller. Other brands of spinners have different center ID's-if you shop around you might just find what you need for cheap.