Stainless Steel Ball Bearings with Ceramic Balls ABEC-5 quality, this is a popular size that could be used in many application that uses this size 3mm x 10mm x 4mm. Bearings are made of Stainless Steel, each bearing has 2 metal shields to protect the bearing from dust or any possible contamination, 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-5 quality, nothing could be better !