Polishing frets. I didn't take any pictures while I was dressing the frets or shaping the nut. I bought a diamond file of eBay for $30. It worked well enough. It is 230/320 grit and it made crowing really easy. I think it could have left a cleaner finish as I still had to sand all the frets a lot to remove the scratches. I will say that it is still much better than my old Gurian file.