Lapping paper: 3M polishing paper and 600g. aluminum oxide
These polishing papers are my go to product for fitting male ferrules. You will receive a half sheet of each grade:
blue: super fine
600grit aluminum oxide paper
I like to cut the paper into strips and then wrap them around the ferrule. For new ferrules I start with the 600 aluminum oxide paper and then move to the finer grades of polishing papers. To get the final fit switch to the blue (super fine) paper and dial in the fit you want. Work slow!
These papers are also great for getting a better fit on pre-fit ferrules. I would start with the grey paper and then move to the blue. You will want to check the fit often to make sure you don't remove too much material.
A half sheet will fit dozens of ferrules. The papers will keep working even when soiled. I have used the same half sheet for multiple years and they still work great.