I actually have a round, 4-pipe hanging rack with a tobacco jar in the middle. Fairly old, bought in a second-hand store. I never hang briars in it, though. Only cobs. But anyway, I agree with Smiff. Measure your hole centers based on your biggest pipe bowl, or the biggest you think you may buy in the future. One inch seems like it would be good for the diameter. Do yourself a favor- make a cardboard mockup or template to check for fit before you bore any holes in wood.