So, you need to drill and run a bolt through a piece of round, square, or rectangular tubing. Did you ever think you have a good chance of collapsing the walls of said tube if you over tighten the bolt or use it to hold something that'll generate stress? An easy way to alleviate the problem is to sleeve the hole with an appropriately sized piece of tubing. Drill the hole to match the desired tubing O.D., tap it into place, and use a washer with an I.D. that matches that of the sleeve/tube, and run your bolt through the tube. This little trick will strengthen your mounting point greatly, and it only takes a couple more minutes to complete.