Check the listing for details. TRB RC 3x8x4mm Precision Ceramic Ball Bearings Metal Shields (2). Condition: New. Listed at 13.26 USD. TRB RC 3x8x4mm Precision High Speed Ball Bearing, Ceramic Hybrid. Chrome Steel 52100 (GCr15) ABEC 5 Races with Ceramic Si3N4 Grade 5 Balls, No Contact Metal Shield. Part SKU# TRB-693ZZ/C Chromium Steel Races Ceramic Si3N4 Balls Low Torque Start Up Dimensions as follows: ID, OD, Width: 3x8x4mm 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.