There is definitely an error in the way you're measuring the bearing bores as the tolerances on bearing dimensions is very tight - a few micrometers at this size.
More worryingly, why are you using deep groove (6000 series) bearings on a ballscrew, not angular contact bearings? If you get the bearings you have to fit they will probably only last a few months since they're not designed to tolerate axial loads. Angular contact bearings are, so you need to get a pair of 7200 and 7201 bearings and the appropriate mount for them, or double row bearings may be acceptable (5200, 5201).