In 
Out3x10x4 Ceramic Metal
Product Overview
The 3x10x4 Ceramic Metal bearing (623ZZC) is a high quality steel/chrome bearing with metal shields and silicone nitride ceramic balls (Si3N4).
A hybrid ceramic bearing 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. These bearings have been tested and proven by the top racers in the world.
