Why do you need these ceramic diff balls you ask? Here are my favorite reasons why. –Less rotating mass (these more than a gram less than other diff balls) –Harder and rounder than comparable tungsten, steel or carbide balls We all want the smoothest, longest lasting diff as possible. These balls do just that. Less rotating mass combined with durability. I could bore you with all the science behind them but the bottom line is that ceramic is better. Make sure you know how many balls your diff takes along with the size before ordering. If you are unsure please check your owner’s manual or reach out to me before ordering. Comes in a reusable snap case. For use in: Associated 5 series Associated 6 series Associated 6.1 series TLR 22 Series Yokomo Xray Many others!