Ok so I have an 18mm/18mm Downstem. I don't have time to order an 18mm glass drill bit, and I can't find any in stores near me. If I used a 19mm glass drill bit , what size rubber grommet would I need?
I'd make it out of a JD bottle, and then take the bottle to a headshop and ask what size grommet would fit. Maybe the guy will fit one in the hole right then and there.