Was reminded of this today when I realized A: I didn't have one and B: I needed one. This thingis for the occasions when you have to shorten a small screw that's already short, or just so small- like the 4-40 in the picture below- that it's hard to hold onto
It's just two pieces of thin, springy steel clamped together at one end- pop-rivet in this case- so it stays together, but not so tight that you can't pivot it open. Drill a hole or two, several if you need for different sizes. You open it up, put the screw in a hole so the head will be between the pieces when they're closed
with the shaft sticking out. Now you can grind or file or whatever without the language practice required when a dinky little screw jumps out of your fingers or pliers. Or burns you when it gets hot.
That steel strap they use to hold bundles of brick & such together works well. You can make the holes just big enough for the shaft to slip in, or in the deluxe version drill undersize and then run a tap in so you can actually screw the screw in for a tighter grip.