S623ZZ Ceramic Balls Ball Bearings, this is a popular size that could be used in many fishing reels, Bearings are made of Stainless Steel, each bearing has 2 metal shields to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease, Ceramic Balls are the highest standard of balls that can make your bearings live at least 5 times more than any other bearings.