New high-speed ball-bearings produced especially for XRAY. ID x OD x level (mm) = 5x12x4. Couple of 2 pieces. Top-quality professional ball-bearings for a super-free, super-smooth drivetrain. These affordable ball-bearings are fitted with unique artificial covers, and tend to be additionally carefully packed with unique oil for maximum smoothness, stamina, greatest limit and maximum performance. These ball-bearings have more (and larger) balls inside the cage versus regular ball-bearings, making them more resilient under lots. Along side it covers are now actually an easy task to get rid of for easy and quick maintenance.