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The hex screw and washer are the only thing holding the wheel in place. So in your circumstance, the wheel is rusted to the axle.
These can be a real bear, but the best initial method is penetrating oil and patience - lots of both. And all penetrating oil is not the same. WD-40, for example is good for a lot of jobs, but this isn't one of them. Use PBlaster, Liquid Wrench (or Kroil if you can get it, it's the best but harder to find). Use a lot, use even more, and let it soak overnight.
If that doesn't work, then another option is to use an air hammer against the bolt to knock some of the rust loose. I've seen good results with that method.
You can also use heat, but use it carefully. Make sure all the air is out of the tires and torch the inner rim where it goes around the shaft while trying to keep the shaft as cool as possible. The heat will expand it enough to clear the shaft if you do it right and luck is on your side.
Best of success. It's not an easy job. When you put them back I'd sure recommend a coating of Neverseez so you don't have such a fight next time.
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