Right Al.
However, when turning finials it seems the steady would best serve its purpose when positioned close to the end, which tends to be the smallest diameter. Intermediate larger diameter sections often have very narrow edges, which would not give the wheels much bearing service.
I know the answer to my question can be mathematically calculated given the diameter of the wheels, but I certainly don't know the formula off the top of my head.
Thanks.
P.S.
I found some .765" ball-bearing shower rollers at lowes.com that would decrease the minimum diameter that the wheels could handle. Cheap too. $5.58 for 4.