The interface of the exterior and the interior of the watch are called the winding stem. The winding stem is the manipulator of the crown to wind and set mechanical movement. The winding stem turns, pulls, and pushes the crown to create the appropriate movement. The crown is attached to the end of the winding stem. The other side of the winding stem is where the winding and setting mechanism of the movement is taking place. There is a square in this end where there is a steady pivot as the winding stem turns.
Many study how to manufacture a winding stem by hand which is quite a challenge. This is a micro-mechanics exercise that entry-level watch makers have to be very patient with.