Here is the working part of the mold, the half that makes the threads. Note the threaded mandrel is spring loaded, so when the mold is opened the threaded core automatically unscrews by the springs pushing against the plate. I imagine that is a modern improvement, which would not be in the older molds that had to be unscrewed manually. Messed up threads would be less likely with the springs than by hand I would guess.

Different manufactures had different methods to make the threads. Sometimes inner skirts were carved into the mold, some are seperate pieces. Look for the flash or mold lines and they will tell you where the parting lines are, but you have to think in reverse! I hope these pics will help understanding of how these jewels were made. Thanks to whomever exhibited it at the San Jose National.