Mountainboard Wheel Bearings: These are Standard bearings to fit a standard mountain board or kiteboard wheel. They fit most boards out there such as MBS, noSno, Scrub, Exit, Bluearth, Kheo, and pretty much any others.... There are 3 different sizes:
6001-2RS - 12mm Axel (Channel Truck) board.
R6-RS - Skate Truck 10mm ATB Axle Boards (3/8in, 9.52mm Axel)
Primo Sk8 - 10mm ATB Axle Standard Hub (MBS Skate Bearings 3/8in, 9.52mm Axel)
The 6001 bearings are used in most boards with spring trucks. The R6-RS are used in most junior skate truck boards. The PrimoSk8 are adjuster bearings to fit nominal 10mm skate (or vector) trucks to standard hubs. Check the picture below and look for the code numbers on the bearings for clues.
Please note the 10mm bearings are not exactly 10mm they are (3/8in) to fit the nominal 10mm or 9.5mm axle mountainboard axles not other applications.