The Revolution Ceramic Series bearings are a low friction bearing with several options to help satisfy anyone's desire. What makes this bearing unique is that it has a rubber seal on one side while having a metal shield on the other. Instead of the steel balls they use silicone nitride ceramic balls (Si3N4). Rubber seals are great protectors against dirt but the price is that they offer a little more friction due to the tighter seal.
5x11x4 Ceramic Revolution bearing by Avid Racing Concepts is the standard bearing for Traxxas Revo clutch and many more. Check your manual for the correct size for your vehicle if you are not certain.