Screw-threaded tube

A screw-threaded tube is a type of case tube with a precise thread on the outside.

In screw-down crowns, the external thread of the tube acts as a counterpart to the crown thread, ensuring that the crown can be screwed down securely and the watch remains water-resistant. A screw-down tube ensures a screw-down, tight, and durable connection between the case and the crown.