Screwed chaton at a movement of
A. Lange & Söhne

A chaton is a movement component.

It is a circular piece of metal inserted in a round hole, in which a ruby is inserted. The ruby is used as bearing for the pin (or pivot) of a shaft of a wheel.

The Chaton itself is attached to the plate, the bridge or the cock by pressing or screwing.

Specifically, from A. Lange & Söhne screwed gold chatons are known. Here the chaton is made of gold and is fixed with two or three (blued) screws.