I have so many files - didn't think I really needed or wanted any more, but this pippin design is such a handy one. I'm friends with a locksmith and I know he has a few of these but I'm not sure how they're used with locks exactly, and I never got to hold one in hand before ordering. It's not real apparent in photos but the sides of this file are not flat but rather slightly convex, which was a slight disappointment for me and my intended uses, but it works beautifully as all Vallorbe and Swiss files do. Knife edge and back are single cut, the back being fairly less aggressive. It's harder to find American mill files with the rounded edges these days but this is a better replacement for wide slots and transitions on work where needle files are just too small - easier to achieve nice edge transitions than with a round file and/or half round. I wish they made this one in an 8-0 or even a 00.