Silicon Nitride Si3N4 (Black) Ceramic bearing.

5 Assorted race cage colours, Red, Green, Blue, Orange, Yellow.

Shield less, deep groove blackened race rings with Omni logo laser etched.

Wikipedia. Silicon nitride ceramic have good shock resistance compared to other ceramics. Therefore, ball bearings made of silicon nitride ceramic are used in performance bearings. A representative example is use of silicon nitride bearings in the main engines of the NASA's Space Shuttle. Since silicon nitride ball bearings are harder than metal, this reduces contact with the bearing track. This results in 80% less friction, 3 to 10 times longer lifetime, 80% higher speed, 60% less weight, the ability to operate with lubrication starvation, higher corrosion resistance and higher operation temperature, as compared to traditional metal bearings. Silicon nitride balls weigh 79% less than tungsten carbide balls. Silicon nitride ball bearings can be found in high end automotive bearings, industrial bearings, wind turbines motorsports, bicycles, rollerblades and Skateboards.