cer188CER188SCPP Silicon Carbide SIC Ceramic Ball Bearings, Dimensions: Bore (Inner) Diameter: 0.25 Outer Diameter: 0.5 Width (Thickness): 0.1875;CER188ZR Zirconia ZRO2 Ceramic Ball Bearings, Dimensions: Bore (Inner) Diameter: 0.25 Outer Diameter: 0.5 Width (Thickness): 0.1250;