There is a leather punch -- available in most hardware stores -- that
punches holes of various sizes. Good tool to have around, as you can
use it to punch holes for leather rivits (repair of handbags, etc.).
Pick the right size (6 on mine) to match the holes you have, and put it
the same distance as the current ones are apart. I find that leather
belts tend to stretch over time, so have regularly added a couple of