Bastard file

I just used such a file to make a door accommodate a new knob. But why is it called a bastard file?

The Oxford English Dictionary defines bastard file as “a file intermediate between the coarse and fine ‘cuts.’” The dictionary notes that as early as 1418 the word bastard was applied to things “of abnormal shape or irregular (esp. unusually large) size”: swords and guns at first, followed by ships, files, type and printed titles, and script. The dictionary’s first citation for bastard file, from Joseph Moxon’s Mechanick Exercises; or, The doctrine of Handy-Works (1678):

The Bastard-Tooth’d File is to take out of your work the deep cuts … the Rough File made: the Fine Tooth’d file is to take out the cuts . . . the Bastard file made.

The bastard file appears then to be that other file, not this one, not that one, neither rough nor fine.

A more fanciful explanation of bastard file appears on a British tool company’s website:

In heraldry, coats of arms belonging to people born outside of wedlock (also known as bastards) bore a device known as the “barre sinister,” a diagonal stripe that ran from the top right of the crest to the bottom left.

This is the same direction that the teeth of a single cut file run in.

That bastard was first applied to things with no resemblance to the barre sinister makes this explanation, to my mind, unlikely. Another fanciful explanation, which brings in a fellow with an unfortunate surname:

The name is a misnomer in that the file was invented by an Englishman named Barsted. When English workers came to the United States and requested a Barsted file, Americans thought this was the English pronunciation for “bastard.”

Richard Pohanish, Glossary of Metalworking Terms (New York: Industrial Press, 2003).

That’s a good story. But it seems impossible to find any trace of Mr. Barsted outside the story of the bastard file. And if bastard was applied to irregular things as early as 1418, this explanation won’t work.

But the bastard file worked, and we now have a door that accommodates its knob.