I used very very old files that my father in law gave me … not intended for nut carving ! very old like 100 year or so / also very very good quality ! these files were used by my grand-father in law who was a professionnal woodworker at the time.
by the way my nut is far from perfect, I made it a little bit too thin. it’s playable but I will very probably re-do another one from scratch but that’s how we learn and this little Jim Harley is a perfect case for this kind of experiment, so no problem !