I always have trouble with stripped off radiator drain plugs, tried all the tricks and end up drilling them out. Today I tried a new (for me) approach and it worked. I welded a large washer to the plug, then welded a nut to the washer.
Forgot to take picture of washer welded to plug.
Hopefully this will help someone else, surely I'm not the only one who gets cubs with boogered up drain plugs.