This NUT will save your bolt

[Make Things]

[NortonDommi]

Rattles my cage big time seeing a file dragged backwards.

[Make Things]

Rattles my cage big time seeing a file dragged backwards.

It was more or less to show how futile it is. Glad you noticed.

[NortonDommi]

Some things were indelibly ingrained from an early age. I know Fireball Tool proved it a fallacy but I will hold with what I was taught and what all the good file manufacturers said in their instructions for use pamphlets.
Another trick for dinged threads is cut a slanting slot across one flat, this turns the nut into a crude die which is usually good enough to clean a damaged thread, also useful for peeling glue e.g. PVA or epoxy. On the larger sizes just cut a slot or two on the inside to just past the root of the thread.
Still a good idea to put a lead on a thread though, far less chance of cross threading. Last one you know doubt know but many learning don't is turn a nut or bolt opposite to direction of lead and you will feel a 'click' as the two thread end pass, change direction of rotation and it will start - great for marking if you are starting a thread under load such as spring pressure.

[Make Things]

I love that there are so many ways to do just about anything. I'll have to remember your tip and try it out. Filing the tip of bolts...many years ago...was what I thought you were supposed to do. It kept me from cutting bolts down and I ended up going to the hardware store for half size smaller carriage bolts. I hope this tip saves someone from my past mistakes.

[Hoosiersmoker]

I usually just take the bolt to the grinder and hold the bolt vertical, cut end down and spin the end against the wheel. This pulls the ragged cut parts down and clears them off as well as giving a tapered lead-in for the nut. Never had an issue.

I also learned that if you have damaged threads on a bolt or threaded rod, just spin a nut on to the bad part as far as you can then lay the nut on a steel table or concrete floor and hit the nut with a hammer on 3 or 4 flats then spin it further on and keep going until all the threads are restored. The nut acts as a die and re-forms the threads as you hit the nut. It works better if the nut is a higher grade than the rod or bolt but it works if it's the same grade, just not lower.