Originally Posted by T-Mar
I can't corroborate that statement, as I don't know the specifics of the die-casting processing and alloys that were used. However, I do know that the ends of the tubes were flared to give some extra insurance against being pulled out of the lugs. The ends of the tubes were capped out of necessity, to prevent the molten aluminum from flowing into the tubes, but the caps also prevented the flared end from collapsing and allowing the tube to be pulled out.
Actually, the tube ends were threaded or serrated and the casting was pressure formed around the threading/serrations to allow the pressure casting to mesh effectively with the tube. I know this because I have cut one of these joints apart with a hacksaw to see how it was done. The joint I cut apart had no flaring.