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I use Blaster on frozen bolts. the main thing is patience. Soak it with blaster, let it sit overnight, then try to turn it gently or maybe pop it with an impact wrench. Once you turn it a fraction your home free. Trouble is, sometimes the head will turn a fraction and the bolt didn`t turn. That's bad news its ready to snap. 9/16" is a pretty thick bolt. I think you can do it. If you can`t move it, just have patience soak it and try tomorrow. Let us know how it turns out.

rich