R2-5Z Stainless Steel Ball Bearings with Ceramic Balls ABEC-7 quality, this is a popular size that could be used in many applications that uses this size 1/8" x 5/16" x 9/64" inch. Bearing is made of Stainless Steel, bearing has One metal shield, Ceramic Balls are the highest standard of balls that can make your bearings live at least 5 times more than any other bearings with ABEC-7 quality.