They are HG (High-Grade) ball bearings to be used on Mini 4WD devices. Versus standard ball bearings, they provide more accurate elements resulting in even smoother rotation gears, axles, and more from your own Mini 4WD automobile.
• HG 620 Ball Bearings x4
• Thickness: 2.5mm.
• suitable for all Mini 4WD and Mini 4WD PRO cars except the Type 1 chassis.