I have cut screw slots using a clockmaker's file, which I bought from Brownell's some 25 years ago. It cuts parallel slots though, not tapered, but narrow. I guess I could make it cut a tapered slot, if I had any need for such, which I don't. That is one unique little file. It will bend in a gentle curve if needed.

I see they do not sell them anymore. I'd better guard mine carefully.

SRH


May God bless America and those who defend her.