I had a spare key with a huge plastic head, and it wouldn't fit where I wanted to put it. I took the plastic off and that left a stub 5/32" by 1/4", and 3/16" long. So, I needed to make a slot in a piece of wood to fit.

I drilled 3 5/32" holes and dug out the material between them with butt of a little file. I then used the drill like a router bit to clean out the slot. I expected the drill to break, but got lucky.

It worked, but it was really kludgy; there has to be a better way. Any suggestions? (I don't know if they make chisels that small, but I sure don't have one)