Grade 25 is normally the highest grade available. The grade number specifies the sphericity of the ball within millionths of a inch. Thus, grade 25 is round to 25/1,000,000 inch. Grade 200 is round to 200/1,000,000 inch, so less round. The lower grade number can also indicate a superior hardness of the ball, relying on possibly a harder steel alloy, or a coating. A grade 25 is hardened throughout the ball, where a poorer grade ball might only be surface hardened. You can expect greater durability from a lower number grade bearing.
Dennis Young working, not riding on a clear cold day in Hotaka, Japan.
> Hi Folks,
>
> Time to do some winter bicycle servicing. I noticed Bicycle Classics
> lists loose ball bearing as grade 25 and the same quality as Campy. I
> have seen other suppliers list grade 200 bearings. How are bearings
> graded? Is a higher or lower number the better grade? Thanks for the
> help!