Anyone know how aluminum pipe sizes work? Is there some kind of
industry standard that manufacturers follow and you can look up (for
finding wall thickness, telecoping lengths, etc)?


For building antennas you want tubing. If you get the tubing with .058 inch
wall thickness then the next size up will slid in with a couple of thousands
of an inch of clearance. Go to here :

http://www.texastowers.com/

and look at their tubing in the online catalog.