When you can't get a nut off a bolt, the threads have probably rusted together. Another possibility might be that the threads of the bolt have been marred or the shaft of the bolt has been bent. The nut won't come off without cutting. Hope for the best, but plan for the worst. Don't waste your muscle strength trying to remove a stubborn nut. Let rust penetrating oil do the dirty work before you try to twist it. The best way to remove stuck nuts is through a series of steps.
Inspect the threads of the bolt for burrs and the bolt shank for bends that could be keeping the nut from coming off. If you find these problems, cut the end of the bolt off with a reciprocating saw. Cut it flush with the nut. If the nut won't come loose after this, move to step two.
Squirt the nut and bolt with rust-penetrating oil. Let the oil soak for 24 hours. Place a wrench on the nut and twist it counterclockwise. Some nuts unthread clockwise, so if you can't get it to loosen one way, try the other way. If the nut won't come off, place a hollow, 4 feet long pry bar over the free end of the wrench. Pry the nut free. If it won't come off, go to step three.
Heat the nut with a self-lighting torch. Heat it until it's red hot. The heat will expand the nut and make it easier to remove. Turn the torch off. Spray the nut with rust-penetrating oil and then try to bust it loose with the wrench and pry bar. If you have access to an impact gun and socket, remove it with that. If neither of these work, go to step four.
Cut the nut off with a reciprocating saw.
