Just wanted to thank Matt again for making such an excellent product... I now have two, and I am already itchin' for another one, haha.
I also wanted to share these images... I know Dirquist posted a pic of his shorty universal... And here are a couple options I have come up with that accomplish a similar goal. I did all of this with a hand drill as a lathe, a broken off piece of utility knife, and a round top Dremel carving bit (held by hand, because I couldn't control both the drill and Dremel at the same time). Most of the major shaping was done with the side/edge of the knife blade while using the drill lathe... I used scotch tape on the drill bit that fit inside the universal or pipe stem tenon so it was snug. The o-ring grooves were done with the Dremel bit, I don't know which number, but it had to be a low 190 series round head engraving bit?
The 306 to 510 adapter and Cherry Vape can't be considered "universal" anymore, but they fit nicely into both the A7 and Phoenix Clones I use, as well as some other devices. They are tight enough that I can bite the stem and not worry about the pipe bowl dropping off, which was the goal. I can understand that a system like this would be hard for Matt to sell on his site, since it wouldn't work with all devices... So basically you need to modify it yourself if this is what you are looking for. The double o-ring stem is what I am converting all of mine into at this point... It still works on a Cherry Vape Universal, or you can direct fit it into anything that uses a standard 510.