I have used every NEW, "Hot set-up",Best stuff EVER,over the years, and all I can say is I have YET to find ANYTHING that out performs KROIL. Alan mentions kerosene and trans. fluid and KROIL is pretty much that. I also recomend to let it soak for a couple of days. Another thing, "rattle" the nut or bolt with a hammer will help getting penetrating oil into the threads. If ALL else fails, heat it up and let it cool a bit then try loosening it again.