· Depending on the form of the grinding media there are ball mills, rod mills, pebble mills and autogenous grinding mills. Grinding media – iron and steel balls with diameter of 15-120 mm, steel or cast iron cylpebs dimensions (diameter and length) of 16 to 25 and 30 and 40 mm, round steel bars with a diameter up to 130 mm and a length equal to the length of the drum.