Skate bearings can be used for most applications within the industry, skateboards, scooters, quads, longboards and inlines all use the same sized bearings, some bearings are measured on an ABEC scale ranging from 1 to 11 (in odd numbers) with 11 being the highest precision, however this does not account for the grade of material used which is also very important to the speed of a bearing. 2 bearings are used per wheel with a spacer in the middle. As usual all the best brands can be found at Skatehut.