High-speed ball-bearings produced specially for XRAY. ID x OD x thickness (mm) = 6x12x4. Pair of 2 pieces. Top-quality expert ball-bearings for a super-free, super-smooth drivetrain. These finest quality ball-bearings are fitted with special rubber covers, and they are degreased and gently oiled with AeroShell Fluid 12 oil for optimum smoothness, longevity, greatest tolerance and optimum performance. These ball-bearings have significantly more (and larger) balls inside the cage compared to the regular ball-bearings, making them way more resilient under loads. The medial side covers are really easy to eliminate for quick and comfortable servicing. These ultra-high accuracy ball bearings are made to withstand all extremes at the track under racing conditions as well as simply fun racing. A "must have" product!