When a flywheel develops wear, it is never out to the full diameter of the clutch surface.
So who ever cuts the flywheel can measure the step on the edge,
and be able to duplicate the step.
But a word to the wise,
measure it yourself, so that you know for sure, and......
be able to check it when the guy hands it back to you.
I have had stepped flywheels handed back to me that were flat (no step),
and I even had one handed back to me with the damn clutch surface below the bolt surface !
(idiot duplicated the worn out surface drop !)
With all that said, I beleave the step is .5mm (.020"),
but don't quote me on that.......