I start out with a small chisel and finish up with a small warding bastard file that cuts a very clean slot. I have worn this file out and have broken the tapered tip off somehow, i haven't been able to find a similar file to buy.
I was in a machinist supply company years ago wanting to buy files, they let me go back in the bins and pick out any file I wanted, I bought a handful of small Nicholson files with the warding bastard in the bunch. Years later when I went back to buy more files the new owners wouldn't let me behind the counter and the lady working at the counter said she didn't have any files like the ones I bought the last time. She didn't go look and I could tell from talking to her she didn't know a drill bit from a Nicholson file.