Reply by casual1carpenter

john, I know how I am when I get an idea stuck in my head, lol. As the hole saw plug will have a pilot hole you could take any square stock cut-off that will go into the tube and drive a pin (larger dia. nail with head removed) and sort of use the stick to the index depth. If you marked the center line of the plug and pre-drilled the tube you might also have a usable visual indicator. good luck with your build.