High-speed ball-bearings manufactured especially for XRAY. ID x OD x depth (mm) = 6x12x4. Number of 2 pieces. Top-quality professional ball-bearings for a super-free, super-smooth drivetrain. These finest quality ball-bearings are fitted with unique plastic covers, and are degreased and gently oiled with AeroShell Fluid 12 oil for optimum smoothness, longevity, highest threshold and optimum performance. These ball-bearings do have more (and bigger) balls inside the cage versus regular ball-bearings, making them far more resilient under lots. The medial side covers are really easy to remove for fast and comfortable servicing. These ultra-high precision ball bearings are created to withstand all extremes within track under battle conditions including simply enjoyable racing. A "must have actually" item!