S6806 Open Ball Bearing Premium ABEC-5 Quality with Si3N4 Ceramic Balls (Silicon Nitride) 30 x 42 x 7 mm S6806 Open Stainless Steel, radial and deep groove ball bearing,bearing is made of Stainless Steel with Ceramic Balls (Si3N4) and Nylon cage,the quality is set to EMQ (Premium ABEC-5 quality) to ensure high speed,inner diameter is 30mm, outer diameter is 42mm and width is 7mm