Ken,?
You may want to carefully inspect the threads on the bar, especially towards the end. Make sure there are no nicks or flat spots on the high points on the threads and that they taper into somewhat of a cone section at the very tip. If you see something you can carefully file out any metal debris inside the thread depressions. If it were me, I would probably wire brush the threads on a wire wheel to polish them down very slightly, after correcting the nicks. Start gently so you don't remove too much metal, and recheck fit.
But then you might have have debris inside the female portion you want to brush out, like Michael said. You could try a toothbrush first, then a brass bristle brush or a steel brush if that doesn't work. Then flush out with WD40 or some GumOut JetSpray carburetor cleaner, followed by compressed air, if you have that.
You probably got some dust or sand contamination in there, common for operations in the dark.
Good luck!?
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