I still don't know what you are talking exactly, you talking about the OD of EACH or the small little balls that are rolling around in the RED circle?But I think you are still missing the OD sphere of the bearings. Even though a thrust bearing does not have an outer race, the ball bearings are rolling/resting on something. Effectively, the centerline of the ball would define the OD of the bearings supporting surface.
If that's the case, I don't agree. The ball only TOUCH the flat surface at a PIN POINT, it's a point contact, OD of the little ball has very little to do with in.