New high-speed ball-bearings manufactured specially for XRAY. ID x OD x thickness (mm) = 5x10x4. Set of 2 pieces. Top-quality professional ball-bearings for a super-free, super-smooth drivetrain. These highest quality ball-bearings are fitted with special rubber covers, and are degreased and lightly oiled with AeroShell Fluid 12 oil for maximum smoothness, long life, highest tolerance and maximum performance. These ball-bearings have more (and larger) balls inside the cage than the regular ball-bearings, making them much more resilient under loads. The side covers are easy to remove for quick and comfortable servicing. These ultra-high precision ball bearings are designed to withstand all extremes at the track under racing conditions or even just fun racing. A "must have" item!