A fusée-and-chain is a mechanical-watch transmission that connects the mainspring barrel to a grooved, tapered cone. As the mainspring unwinds and its force falls, the chain moves across changing radii on the cone, altering leverage to help even out the power sent to the watch’s wheel train.
What are the fusée and chain?
The fusée is the cone, cut with a spiral or helical groove. A fine chain runs between it and the mainspring barrel, which contains the spring that stores energy. Together, the parts transmit the spring’s power to the wheel train.
The Metropolitan Museum of Art defines the fusée as “a cone with a spiral groove in its surface” that accommodates a cord—or, later, a chain—running between the spring barrel and the cone. The museum’s explanation of watchmaking describes the mechanism and its historical use.
How does a fusée and chain work?
- The mainspring unwinds. It releases energy from inside the barrel, but its force changes as it runs down.
- The chain transfers that force. It connects the barrel to the fusée and travels through the cone’s groove.
- The effective radius changes. As the chain moves along the tapered cone, it acts at a different distance from the fusée’s axis, changing the transmission’s leverage.
- The wheel train receives compensated power. The changing leverage is intended to help offset the spring’s falling force and deliver more even power to the going train.
This is compensation, not a guarantee of perfectly constant force or perfect timekeeping. A. Lange & Söhne notes that the mechanism reaches limits when the spring is near both fully wound and fully unwound. The maker describes its fusée-and-chain transmission as a complication intended to improve a mechanical watch’s rate accuracy.
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Why did watchmakers use it?
A mainspring does not deliver identical force throughout its run. The fusée’s changing leverage was a way to compensate for that variation mechanically, before the spring’s power reached the wheel train. It was especially significant in the history of portable precision timekeepers.
The Foundation de la Haute Horlogerie says that almost all watches of the sixteenth, seventeenth, and eighteenth centuries had a fusee. It dates the replacement of gut with chain to around 1640. Museo Galileo describes linked chain as gradually replacing gut from the mid-seventeenth century. These are dates for the transition from cord to chain, not an agreed date for the invention of the fusee itself.
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The Metropolitan Museum of Art says the mechanism remained in use in portable precision timekeepers until the mid-twentieth century. Today, modern spring materials and other approaches have largely displaced it, though some watchmakers continue to use the transmission. Monochrome Watches’ glossary explains its historical role and why it became less common.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Is the mechanism still used in modern watches?
Yes. It is not exclusive to antique watches: some contemporary high-end mechanical watches retain a fusée-and-chain transmission. Modern examples have been associated with Breguet, Zenith, A. Lange & Söhne, Cabestan, Romain Gauthier, and De Witt, among other makers. Monochrome Watches’ overview of modern examples documents these uses.
Those examples show that the mechanism survives, not that it is widespread or demonstrably more accurate than other designs. The sources cited here do not provide comparative test figures that would establish a quantified performance advantage.
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