The 5x11x4 Ceramic Metal (MR115ZZC) bearings are a high quality steel/chrome bearing with metal shields and silicone nitride ceramic balls (Si3N4). These bearings have been tested and proven by many racers.
5x11x4 Halo ceramic bearing by Avid Racing Concepts is a popular bearing for 8th scale buggies like the Losi 8ight, Kyosho MP9, and Hot Bodies D8 as well as many helicopters.. A ceramic can spin at higher rpms with less drag and the life of the bearing is far greater than a steel bearing but in our industry we suggest that you maintain them with oil or grease every half-gallon to a gallon for the longest life possible. Another benefit to ceramics is the weight difference in the balls allowing for less rotating mass.