Under the Loupe/How to Remove a Threaded Crown Tube
Crown tubes that are threaded and must be screwed into the watch case are almost always secured in place and made water-resistant with thread-locking glue. As the walls of these tubes are made of relatively thin steel, it is easy to shear the tube in half when trying to remove it. In order to remove the tube safely, it is advisable to break the bond created by the thread-locking glue by applying heat to the tube. A more consistent and precise way to apply this heat than using an open flame, is to insert the tip of a soldering iron into the tube and turn it on. Once the case around the tube is hot to the touch, remove the soldering iron and proceed to remove the tube using the tool designed for the particular crown tube you are dealing with (often a square or hex key).