For a long time I have had many conversations regarding the grading of Si3N4 Balls and the relative benefits of each manufacturer. Im not hear to bang on about who makes the best but to try and clear the issue up, I wont even mention what grade ours are but you can find it on our data sheet.
There has been a huge amount of incorrect thought bandied about by people and often pushed by those selling them.
I have seen people make up grade numbers related to the ABEC scale which bears no significance to balls specifically but to an assembled bearing.
I have also seen people who have bought grade "X" or "Z" balls claim theirs are superior as the number is higher than brand "A" without realising that the ABMA grades are inverted to what you would expect of an ABEC rating. I have seen people proclaim grade 7 - which dpes not exist in the ABMA scale. I have seen people claim that theirs are the best as they are grade 5, therefore superior to grade 3.
As far as we are aware, all manufactures work to the recognised ABMA grading stsyem for spherical balls. There is no debate about grading systems for spherical balls.
There is more info on Wiki
http://en.wikipedia.org/wiki/Ball_%28bearing%29#Grade
And a variation on the Wiki page from when we initially launched our own Si3N4 Balls
http://www.answer-rc.com/downloads/C...ta%20Sheet.pdf
Hopefully that really does clear things up..