No, not some painful medical condition.

Just a simple device for holding small pieces of work while you file, or do other work on them.
Easily made from whatever bits of steel happen to be available, I must have made dozens of the things over the years, in all sorts of shapes and sizes. Would be surprised if many members here hadn't knocked up something similar?

Used like this for cross-filing.

Or this way on for draw-filing.

Or like this for edge filing.

I'm sure I don't need to explain to anyone on
this forum how it's made. But here's an assembly shot anyway.

Can even be used as a light drilling fixture, as long as you don't mind ending up with a few holes in the base plate. Will also hold round stock more securely if you file a v-notch across the face, and a matching one on the under side of the finger itself.
one_rod.