1000, 1500 and 2000 grit sand paper.
A number 4 and 6 Swiss Grobet files. These are super fine and the filings are barely visible.
And of course a metal lathe. Not shown is 0000 steel wool. Ferrule fitting can be done with sand paper only, files only, or both, which is my preferred method. The process is very simple: take metal away in very small steps, stop and measure, repeat. As we get closer to the female dimension it’s time to test the fit every time we stop to measure. Patience pays off, lack thereof will get you a big OOOOPS moment, make you use bad words and get you to order another ferrule. NOT GOOD!