Taper Pin Reamers, 3-13mm Bridge Pin Hole Hand Held Reamer T Handle Tapered 6 Fluted Chamfer Reaming Woodworker Cutting Tool (1/8-1/2)

Worked like a charm. I needed it to make the peg holes bigger in my custom bass. It's not nearly as sharp as it could have been, but it worked. I can't complain too much. I will say you need to use at your own risk. Also if you're scared of using it, you should test it first before applying too much pressure to your project. I was super careful on the first hole, and put a piece of painters tape where I needed to stop for the other 3. Done in 10 mins or less.

Has been great to have when I need to increase the size of a hole in one of my guitars. Maybe you're swapping pots and the new one have a bigger shaft. Or your painting or finishing a guitar body and your got stuff in the holes. You can use this to easily remove it without having to get out a drill motor.