HSC - HSC CERAMIC bearing 6805-RS 25x37x7mm 19.5g

The HSC Ceramic  ABEC 5 bearings have ceramic balls and steel races.

Balls:
Silicon Nitride Ceramic Si3N4 balls are made from pure Silicon Nitride material with extreme high density from uniform compaction, the micro-structural development of this material during manufacturing is second to none. These high precision grade 5, Si3n4 pure ceramic balls are 5/1,000,000″ from exactly round in sphericity, 60% lighter weight, and 7 times harder than steel.
The balls are Grade 3, Silicon Nitride (Si3n4).  These are the roundest balls you can buy without a military license.

Races:
52100 High carbon Chromium Alloy Races with Cryogenic Treatment:
Cryogenic treatment takes the races down to minus three hundred degree Fahrenheit to normalize the crystalline structure of the material so the races will resist the hardness of the ceramic balls and get the maximum wear potential.
The races are treated with a black oxide coating, which helps prevent rusting in the bearing. The races are then reground to a mirror finish after this treatment. Finally, they are cryogenically treated for strength before assembly.

Seals:
RS with low friction