Well of course you knew what a "crush tube" was! didn't you???

Since somebody asked---If you have to bolt through a peice of rectangular tubing to attach a bracket, etcetera to it, as you tighten up the bolt, the wall of the rectangular tube will begin to collapse. You want to tighten the bolt good, but not wreck the tube, so---you drill a hole thru the rectangular tube and weld in a peice of round tubing with an inside diameter slightly larger than the bolt you want to use. Now, when you torque down a nut on the bolt, the welded in round tube will keep the rectangular tube from "crushing". This is a favourite method used on rectangular tubing chassis.---Brian

I use this alot from my old race car days til now with rods.

If its a low-stress attachment, you don't even have to weld anything, Just drill the "off-side" hole large enough to insert the pipe, leaving the other side to hold the bracket or whatever. It's as strong as a bolt through the one wall, the OEM's use it all the time, and it looks better than a big hole that lets the tubing fill up with crud.