I made (well, I designed and had it laser cut) this simple tool to act as a guide for the holes for a teapot spout:

Here’s a guide with a few different sizes you can print at home. I made it A6 so it can be printed 4x on an A4 page (sorry Americans, it won’t fit so neatly on US paper sizes) for people who want multiples.

Link to PDF

The one that looks like a target is in case you want to use a different sized drill bit/hole cutter. The lines are 1mm apart. Just mark the centres of the holes in the clay when it’s leather hard, then either drill them or use a hole cutter.