Fusee A fusee is a cone-shaped pulley with a helical groove around it. Part of the movement of early spring-powered mechanical clocks and watches, it improved timekeeping by equalising the uneven pull of the mainspring as it ran down. The origin of the fusee is unknown. Fusee-like mechanisms were being used as early as the 1400s in weapons, and the earliest known fusee clock appears to have been made around 1430.
