category: skateboardbearings brand:pig
Skateboard Bearings Sizing Chart
In selecting your skate bearings you need not worry about any sizing. All wheels require the same diameter of bearings and other than some home made bearings all should fit.
Of note for bearings is the ABEC scale for which all have a ranking. It is a method of rating the manufacturing tolerances of the bearings. In short the higher the ABEC rating the tighter the tolerances thus the more expensive bearing.
So to drive it home; the higher the ABEC rating the better the bearings.