Amen on the thank yous, both for the question and the answers. It brought back memories of fighting with ultra fine threads (which I think contribute to the tightness more than the corrosion, etc.) I recall trying to remove very slightly crossed threads on Oxyacetyllene bottles. If you have ever had the misfortune of cross-thredding the cap on one of those bottles , you will know I mean. It required a large pipe wrench, an eight foot pipe. a large six foot bar in the pipe, a still another several feet of pipe over the bar, too loosen the bugger, and it was tight most of the way, once it became cross-threaded with those fine threads. Had to have the pipe wrench at 11 o'clock due to the slack in all those levers. I think I should have tried to tighten it more first, in order to get back on straight threads a little easier? As I recall, it was the female threads that were buggered, and I threw that cap away where nobody would ever find it!
How about a flashlight of vintage origin? To this day I have a neat old three-battery policeman's flashlight that I pretty much ruined in trying to get the lense cover off! Again, you just can't get away with much if you cross-thread very fine threads even a little bit. I decided I would put a slice across the threads vertically with a dremel to try to save it, but i probably will never recover the light, since I buggerd it quite badly
I tried removing the sacrificial rod on a water heater once. I give up after extending several feet of cheater. I think in this case it is coarser threads, but corrosion welded things together (AFTER ALL, THAT IS THE PURPOSE OF THE ROD, TO corrode selectively)! If I run into such hardships again, I will access this web page and try some of the suggestions. Congratulations on getting your hub-cap off. Did you have a regular hub-cap wrench initially? I hope you'all get something out of my rambling, besides staying clear of me--HO!