9 mm and a bore diameter Less than 10 mm are known asExtra-small ball bearings. Standard ball retainers (cages) are made from pressed steel. Machined cages are used in bearing operating atvery high speed or for large diameter bearings. Deep groove ball bearings with seals or shields are standardized. They contain proper amount of grease inadvance.

6001 Nachi Bearing Open C3 Japan 12x28x8 Ball Bearings