It is called a Tap and Die set. It resets the threads on the shaft. now look it up.
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Get the Dye. Take the nut to match the correct size. Don't just buy a kit and hope the right size is in it.
Make sure there is NO grease on the Shaft Threads when installing the nut. it needs to be completely clean to avoid what just happened.
That is the same nut that was on the old prop isn't it? There are a few different thread patterns for different lowers. Some metric and standard are Real close but cannot be interchanged. They will start then bind up.