And here is on a Dale / Thiersch style. The PVC inside diameter is 34mm, and these capsules are slightly smaller ~32mm. I put a 'liner' of brass 1/4" stock inside the mount with a wire soldered on for the backplate connection that filled the gap and secured the capsule as the screws are tightened.
I switched to set screws after I took this picture. The PVC threads really well and seemed to work fine. Again I could have sanded this down to make it less bulky.