I bought these about a year ago & keep forgetting to share; these are diamond-impregnated files, grits ranging from 40 to 600 grit, in coarse, medium and fine increments (two each). They're a little more expensive now than they were (I paid about twelve bucks), but still a great deal for what they are, and compared to "luthier" branded tools I've seen. I've found them to be extremely useful.
I also found that the width of the files is almost perfect for 'ramping' compensated saddles for intonation...can actually compensate individual strings across the width of the saddle with these.
https://www.amazon.com/SE-74336DF-Fl...3344862&sr=8-5