S6001 Open Ball Bearing ABEC-7 Quality with Si3N4 Ceramic Balls (Silicon Nitride) 12mm x 28mm x 8mm S6001 Open Stainless Steel, radial and deep groove ball bearing,bearing is made of Stainless Steel with Ceramic Balls (Si3N4) and Stainless steel cage,the quality is set to EMQ (ABEC-7 quality) to ensure high speed, inner diameter is 12mm, outer diameter is 28mm and width is 8mm.