Jay, my plan is 'no threads'. I want to use the o-ring method. The o-ring (a standard hardware store item) sits in a groove in the base of the bowl and 'screws' into the threads in the pipe. Yes, the threads are proprietary. They are a '4-start' thread, meaning the bowl screws in with a quarter turn.
This is a bowl being turned, image from 'net.
Wiz, IF I succeed in making bowls, I won't be selling them. I will be giving them to members here, just because. Watch for progress. I got my lathe set up this week, still need to get the band saw going and will pick up a small drill press on Monday, I hope. I have a complete machine shop, but it is still in storage 150 miles from me. I won't be able to move it until next year sometime... I hope it happens anyway.
So, when the wood shop gets going, I should be making some goodies.
Here is a blog that documents the bowl making process. Part 1 is shown, part 2 is the next blog entry.
http://hobopipes.blogspot.com/2013_08_22_archive.html