New high-speed ball-bearings produced especially for XRAY. ID x OD x level (mm) = 5x12x4. Set of 2 pieces. Top-quality expert ball-bearings for a super-free, super-smooth drivetrain. These affordable ball-bearings are fitted with unique synthetic covers, and so are gently loaded with unique oil for maximum smoothness, endurance, highest tolerance and maximum performance. These ball-bearings have significantly more (and larger) balls within the cage compared to regular ball-bearings, making them more resilient under lots. Along side it covers are now simple to remove for quick and easy upkeep.