S687ZZ Premium ABEC-5 Stainless Steel Ball Bearing 7mm x 14mm x 5mm with Si3N4 Ceramic Balls (Silicon Nitride) S687ZZ Premium ABEC-5 Stainless Steel Ball Bearing, Bearing is 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.