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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.