Kind of interesting to read their comments on mill files; "Principally used for sharpening mill-saws; also mowing machine knives and plows; in machine shops for lathe work, draw-filing, and, to some extent, finishing the several compositions of brass and bronze."
It seems like 3/4 plus files one finds these days are mill files of various sizes, with the triangular files making up a significant portion of the remainder. This is true even when I am combing through boxes of old files at the flea market, where one would expect more variety among the shapes. I wonder how the mill file, which seems like a more specialized shape than a plain old flat file, became the default standard?