I believe solo stems fit the herbalaire, but prbly not that tight.
I took some measurements and photos of my broken gong adapter.
So yeah it's all about that cylinder with all the measurements. After the tight point where it's 0.5345 you can really do whatever. It seems like the diameter actually decreases ever so slightly from the left to the right in the picture. As long as you aim for 0.62inches it should be fine I think. I forgot the inner diameter, but that doesn't matter anyways. Only the outside diameter and the length of the cylinder matter really when it comes to numbers. The point of constraint doesn't need to be to exact, there just needs to be some.
This is how it sits in the HA
The glass is a little hard to push in, often I need to start the HA, so things warm up and only then the glass goes in all the way. Once it is all the way in it hits the bottom of the heating chamber, you hear like a little click. The chamber is just a steel cylinder on the inside. The white stuff in the photo is teflon. I believe the teflon has a slightly smaller inside diameter than the rest of the chamber. That's what locks the glass in I assume. Looks like the constraint in the glass is right where the teflon is.
Here is just some more photos..