gradings of ceramic diff balls

[johnnyp]

recently posted by a retailer on oople

For your reference:
The ABEC scale is an industry accepted standard for tolerances.
ABEC = Annular Bearing Engineering Committee

ABEC 1: 0.0075mm (0.000295")
is the most crude, the least precise, and the cheapest
ABEC 3: 0.0050mm (0.000197")
is what is mostly known as cheap. Won't roll very smoothly or fast.
ABEC 5: 0.0035mm (0.000138")
these are the normal grade that the majority buy and what normally one finds on the market
ABEC 7: 0.0025mm (0.000098")
would be very fast and ultra smooth, but very expensive. Although extremely suited to RC and very long lasting, there is a risk of needlessly damaging them if you over tighten your diff.
ABEC 9: 0.0012mm (0.000047")
the highest grade and ridiculously expensive

this information is correct for bearings however the balls we use for ball diffs are in silicon nitride and come under there own gradings known as AFBMA


AFBMA Std 10 - Principle Tolerances

the standard available grades are grade 5 and grade 25
in laymans terms the grade 25 bearings are too 1 micron in roundness and the grade 5 is too a quarter of a micron in roundness and tolerance over a batch
so a true grade 5 diff ball bearing is too a tolerance in roundness and overall diameter of .25um and 1um is 0.0000001
unfortunately somewhere along the lines there seems too be some confusion as ABEC is the wrong grading too use

hope this clears up the confusion about diff balls
john plummer
CPD Racing