When were the ABEC spec's first published? I would guess today just
about any new machine used to make ball bearing is 1000X better than
is was back then. A manufacturer would have to screw up bad to make
an ABEC 1 today, IMHO.

Thank You,
Randy

Not really - up through a 50 mm bore there is only 1 to 2 micron
difference in the allowable bore tolerance between each grade. For
example, a 50 mm bore ABEC -1 has a tolerance range of 0 to -12
microns whereas an ABEC-3 is 0 to -10 and an ABEC -5 is 0 to -8. If a
manufacturer allows their tolerances to float across the range there
is little difference between the ABEC grades. Since most try to stay
in the middle of the range then drifting off 4 - 5 mm would be
substantial though.