The centerless ball grinding method is the one used commercially. In this process a multitude of blank balls are fed between two annular ring shaped plates, of which one is rotating and the other is held static. The basic principle of this process is based on the gradual averaging of errors. Theoretically the three largest balls between the plates at any one time will receive the full load of the plates, and will therefore be quickly abraded. As the process goes on the variation in the size and in the roundness of the entire lot of balls decreases. One full load of balls produced on a commercial ball grinding machine varies from 500 to 1000 pounds. As you can see by the numbers involved, this is a very productive process.