LittleMachineShop.com - Mini Mill Spindle Box Assembly R8

What size of bearings does this use?? What is the highest speed you could run this spindle without extra balancing? assuming the bearing RPM was not the limiting factor because you swapped them out for angular contact bearings?

10,000 rpm? Less? More?

If i knew the size of the bearings i could search for some bearings!

Thank you.