Brand new high-speed ball-bearings produced particularly for XRAY. ID x OD x depth (mm) = 5x12x4. Set of 2 pieces. Top-quality expert ball-bearings for a super-free, super-smooth drivetrain. These best value ball-bearings are fitted with unique synthetic covers, and so are lightly filled up with unique oil for maximum smoothness, stamina, highest tolerance and optimum performance. These ball-bearings do have more (and bigger) balls within the cage compared to regular ball-bearings, making them a lot more resilient under lots. Along side it covers are actually simple to remove for quick and easy upkeep.