TRB RC 2pcs 15x21x4mm Precision High Speed Ball Bearing, Ceramic Hybrid. Chrome Steel 52100 (GCr15) ABEC 5 Races with Ceramic Si3N4 Balls, Hybrid Seals with 1 No Contact Metal, 1 Low Contact Rubber Seal Yellow.
Part SKU# TRB-6702-RZ/C-YE

Chromium Steel Races
Ceramic Si3N4 Balls
Low Torque Start Up

Dimensions as follows: ID, OD, Width: 15x21x4mm

This Bearing is Compatible with Part #:
Axial: AXA1243
Arrma: AR610018
Losi: LOSA6944
Mugen: E0601
Team Associated: 89162

The Characteristic of Ceramic Balls

Compared with steel, ceramic materials are noted for their better or particular characteristics, such as wear-resistance, corrosion resistance, high temperature resistance, electrical insulation (except SiC), non-magnetic, high strength, high rigidity, and low specific gravity. These properties qualify them for replacing steel to make bearings serve in conditions of higher speed, harsh environment and less lube, and decrease wear, noise, vibration and maintenance time of bearings, and eventually increase performance, reliability and life of bearings.

And a properly engineered silicon nitride bearing ball fails in the same manner as a steel ball, flaking of the ball surface.