What he did was this:
First he drilled holes in the aliminium tube just big enough for the but to fit in. Then He got a hplastic tube and put it inside the aluminium tube. Then he drilled a hole just big enough for the bolt (but not the nut!). Then he put the chain inside the plastic tube, which is inside the metal one, and stick the bolt through all the holes and out the other end. Then, he screwed the nut up really tight, and it should be kinda embedded into the metal. Then saw off the remaining bit of the bolt, and hit the end of the bolt with a hammer to musroom it out.