Different types of grinding media are used for various grinding applications. Grinding balls are one type of grinding media used to reduce particle size in mills and are available in various sizes, shapes, and materials like cast iron, steel, and ceramic. Other grinding media include rods, beads, satellites, and specially shaped items. The type of grinding media chosen depends on the material being ground. High-density media made of alumina oxide is often used in pebble and ball mills. Cylpebs are another type of grinding media but are less common and more expensive to produce.