You can use a thread pitch guage. Little tool, sold at hardware stores. I believe Puch is Austrian, which likely means English threading. You can also try to put a cup of known threading into the shell, but do not not not force it. Another way is to put a cup of known threading next to your cup and see if the threads match, if they do, you will be able to press them together and the threads will insert perfectly into one another. Hold up to light to make sure they are fitting together.