tube size slides over scaffold tube

I made a table to make sense of the confusing sizes of USA pipe, fence post, electrical conduit, DOM tubing etc by combining product listings from the manufacturers' websites.
Chain link fence posts here have the same ODs as water pipe despite different size designations, while thin-walled EMT conduit has the same IDs as Schedule 40 pipe, so some sizes of EMT may telescope into fence posts if the welding flash doesn't interfere.
For example, 1-5/8" fence posts have the same 1.66" OD as 1-1/4" pipe and an ID of 1.53". 1-1/4 EMT conduit has an OD of 1.51" and the same 1.38" ID as 1-1/4" pipe. Stronger fence posts with thicker walls are available.
I was in line (queue) at an industrial supplier behind an alternate energy inventor who had special-ordered 2.000" ID ball bearings for the 2" water pipe supporting his tracking solar array. He got a nasty surprise when he received them and tried the fit; 2" pipe is 2-3/8" diameter and not very round.