Sheffield File Cut Grades
A scale of coarseness with no numbers in it at all.
Origin
Established by the Sheffield cutlery and edge tool trades, and in continuous use since the eighteenth century.
The catch
Bastard is not an insult but a grade, sitting between rough and second cut. The scale is entirely ordinal, has never been numerically defined, and is still what you will find printed on a file bought today.
Rapid stock removal on soft metals. Leaves a surface requiring considerable finishing.
General heavy shaping.
The workhorse grade, and the one most commonly stocked. Not a comment on the file.
Shaping and fitting where some finish is wanted.
Finishing work. Leaves a surface ready for emery.
Final finishing on precision work, and on hardened steel.
The grade describes the spacing of the teeth, but relative to the file’s length: a bastard cut on a twelve-inch file is coarser than a bastard cut on a four-inch one, because the teeth are spaced proportionally. That makes the scale genuinely relative rather than absolute, which is unusual and slightly maddening, and it is why filemakers never converted it to numbers. Sheffield still produces files to these grades, as it has for two and a half centuries.
On the evidence
The grade names are continuous, but their meanings are not necessarily so. Tooth spacing varied between makers, and a bastard cut from one Sheffield firm was not identical to a bastard cut from its neighbour. Because the scale was never numerically defined, there is no way to check a modern file against an eighteenth-century one beyond comparing the objects themselves. The vocabulary has survived more reliably than the standard it described.