I read on the Ishiwata 022 seat tube is 0.6mm thickness of the non-butted sections so it's paper thin


Just found this it's 1-inch dia looks about right size hope I don't have to use it. I was going to dump it many years ago I knew it would come in handy one day. I do have a .5 inch drill chuck somewhere

I once read on light frames bikes they make tubes different thickness's, seat tube would be thinest since it's in compression.