Unless I am misunderstanding this discussion, it seems like an awful lot of back-and-forth for a very simple problem.
HO scale is 1/87 actual size. Simply divide the dimension of the real-life object by 87 to get the size you need for your HO railroad.
Example:
Let's say a real-world light pole is 10 inches in diameter. Then the HO light pole should be 10/87 = 0.115 inches (to the nearest 0.001 inch).
You probably won't find tubing that is exactly 0.115 inches in diameter, but 1/8 inch tubing (0.125 inches) is pretty close. If you have access to metric sizes, then 3mm tubing (0.118 inches) would be even closer to 10 scale inches. But I doubt anyone will criticize if you use 1/8 inch tubing to represent a 10 inch light pole.
Again, just divide the real-world dimension by 87 to get the HO equivalent for the dimension.
Of course in the real world, light poles are often tapered, but finding miniature tapered tubing will be difficult and expensive!
- Jeff