Ball Bearings 9mm x 18mm x 4mm Open Ceramic Stainless Steel Stainless Steel Ball Bearings with Ceramic Balls, this is a popular size that could be used in many application that uses this size 9mm x 18mm x 4mm. Bearing is made of Stainless Steel, Ceramic Balls are the highest standard of balls that can make your bearings live at least 5 times more than any other bearings.