6x12x4 Ceramic Revolution

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.

6x12x4 Revolution Halo bearing by Avid Racing Concepts is a popular bearing for vehicles/makes like the T-Maxx, E-Maxx, Tamiya's, and others.