Ball Bearings 6203-2RS-5/8, the inner diameter is .625 inch, outer diameter is 40 mm and the width is 12mm. This is a popular size that could be used in many applications, Bearings are made of Chrome Steel and can rotate up to 15000 rpm, each bearing has 2 Rubber Seals to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease,Radial Deep Groove Ball Bearings - Size: .625" x 40mm x 12mm - 6203-2RS-5/8" - ID=5/8 inch (bore) - OD=40mm - Width=12mm - Type: Deep groove ball bearings - Closures: Rubber Sealed - Lubrication: Self Lubricated (Grease)