enfield,
I do not understand the loose terminology unless
you are speaking of the spacer balls which
are sometimes used to separate the load balls
instead of a cage or spacers. Most load balls
are matched sets and made to fairly accurate
tolerances, probably grade 100 or grade 50
depending on the ball diameters.
Are you speaking of inexpensive bearing made
outside of the US or what? Even the more
notable bearing manufacturer's are going out
of the country to manufacture their product.
I have seen balls from China that have not met
the AFBMA standards for quality. But as the chart
shows on Israelkk's posting, you can buy balls
of many different grades depending on the application.
The C_ values are the internal bearing clearances
rather than ball quality levels.