S6903 Open Ball Bearing Premium ABEC-5 Quality with Si3N4 Ceramic Balls (Silicon Nitride) 17mm x 30mm x 7mm S6903 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 (Premium ABEC-5 quality) to ensure high speed, inner diameter is 17mm, outer diameter is 30mm and width is 7mm.