Thanks, I considered counterbore tools before and you are right that it might be the best choice for a problem , particular engine whose threaded output shaft is some undersized. It was for the Super Tigre GS-40 that I bushed a prop before. I have the equipment for doing that and it is a relatively fast straightforward job.
I still don't have an answer to my original question about the actual sizes of the Great Planes step reamer. Possibly my referring to metric dimensions kept someone from measuring with an inch mic. Measurements in inches would be fine for me, it's an easy calculation.
Thanks for all the above responses.
Dan