Hello! I've used Kano-Kroil for years now, I recently found Aero-Kroil @ Napa. We used it to take the bolts off of old tractors. I believe it's about as good a penetrating oil as you can get. I also use PB blaster, and Marvel penetrant, but I like Kroil the best. If the nut/bolt is huge, let it go a little while, or overnight for best results. Cabela's also has it. Thank You, LRW.