Fusee

(fu-zē'), n. [Fr. fusée, a spindleful, squib, rocket, fusee; from Pr. fus, O. Sp., Pg., & It. fuso, Fr. fuseau, Lat. fusus, spindle.] The cone or conical wheel of a watch or clock, designed to equalize the power of the mainspring by having the chain from the barrel which contains the spring wind in a spiral groove on the surface of the cone in such a manner that the diameter of the cone at the point where the chain acts may correspond with the degree of tension of the spring.

F, fusee. B, barrel.