Repairing a "Burred" thread

If the threads on a bolt look good but your nut will only start and not go on all the way, and you are sure it is the correct nut for the bolt or stud check for any burrs on the bolt. A quick way to repair a burr without the proper thread die or thread file, is as follows:-

Take some valve grinding compound and put a little on the male threads of the offending fastener. Run the nut onto the fastener until it stops, then back it off.

Then repeat this continually until you start getting the nut to fit. You may have to clean and re-apply the compound if it gets too dry, but you can do that no problem. You can feel the nut going a little further and further each time you turn it.

At the end you should get the burr off the thread and be able to tighten the nut down without damaging any more threads.