I am unsure about the correct reference to apply to my cues that have 3/8-10 pins. One is a McDermott and the other a Spitz. The profile of the thread differs. The Spitz shaft screws a few turns on the McDermott and then began to seize so I recognize they're incompatible. In the future I would like to buy extra shafts that have the correct thread. What is the difference ?