So I'm curious about where you got the dimensions for the wheel bearings, actual measurements or a website? I don't have any experience with Chinese crap but if I use a 1/2" bearing, a 1/2 axle will fit. Now if I take a mic to either, neither will actually measure .500" that's because two parts can't share the exact same space(size) there will be a certain amount of clearance.
There is also the question of nominal measurements vs. actual. a bearing measuring 15mm ID may not actually be 15mm exact. and an axle measuring 14mm may not be either. Again, where did you get the measurements you are quoting?