5 x 10 x 4 Stainless Steel Dry AEEC-5 Ball Bearing With Ceramic Balls (Si3N4) 5mm x 10mm x 4mm 5 x 10 x 4 Stainless Steel Dry AEEC-5 Ball Bearing, this is a popular size that could be used in many fishing reels, 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.