Size Reduction Resource Center. Listed below are some helpful links to educate you on your process equipment decisions. Ball Mill Application and Design. Mill Refurbishing and Rebuilding. Ball Mill Loading - Dry Milling. Mill Speed - Critical Speed. Ball Mill Loading - Wet Milling. Pebble Mill Application and Design. Ball Mill Ball mills crush material into various sizes and extract resources from mined materials. Pebble mills are a type of ball mill and are also used to reduce the size of hard materials, down to 1 micron or less. Because of their fairly simple design, ball mills and pebble mills are less likely to need costly repairs (unlike other crushing or extraction equipment) making them an attractive option for businesses on a budget.