It was a lot of years ago so my memory is rusty. I had a very early MBW 1665 and wanted to install a gen crown and tube. IIRC, the tube came out of the case with a triangular file pressed in the opening to unscrew it. I used a tap to chase the threads and clean them up a bit, they were the same as my gen tube, and quite messy. I unscrewed the old crown from the stem and the new crown screwed right on. I did a test fit and decided the tube should be countersunk a little so I put a big drill bit in my Dewalt and opened up the tube thread a little. I added a bit of red Loctite, screwed the tube in, then screwed the crown onto the tube and cranked it down until the crown bottomed out against the case. Perfect fit and it never leaked a drop. Total elapsed time, maybe 30 minutes.