Oh goodness.... sometimes there is no winning.... you have found yourself in a very specific situation worst case with broken bolts came down to drilling till the threads just start showing them picking them out with a dental pick.... you cant even do that. Without the aid of heat it seems your up the creek, as they say.Thanks, but you're correct in that it just "riveted" the thin wall tubing into the larger tubing it was sitting in. In this case both tubes are under the curling ice for my Crokincurl game board (basically I've converted the larger game like they are using at the Forks in Winnipeg to half a normal curling sheet and I've set an angle iron frame under the ice to hold the "pegs") so welding is not an option. Plan B was to thread the inside of the tubing with 7/8" bolt threads. I put a 5" bolt down into the tubing with a large washer on it to pry the tubing up with 2 pry bars. No dice. Plan C was to drill a 1" hole in a couple of 2x6's and use the thread to draw it up as I tightened the bolt. I used a 3/4" breaker bar with 3 ft of tubing on it and decided to quit before I broke the bolt off in there too. I tried drilling it out with a 1" bit, but the rough top of the broken tube kept catching the drill bit and shaking it loose even with a really good Jacobs chuck. Apparently the broken tubing is staying there until the ice melts in the spring so I dropped a broken bridge bolt down the center to hold things in place until I can fix it right.