A
mainspring is a spiral
torsion spring of metal ribbon - commonly
spring steel - used as a power source in
mechanical watches, some
clocks, and other
clockwork mechanisms.
Winding the timepiece, by turning a knob or key, stores
energy in the mainspring by twisting the spiral tighter. The force of the mainspring then turns the clock's wheels as it unwinds, until the next winding is needed. The adjectives
wind-up and
spring-powered refer to mechanisms powered by mainsprings, which also include kitchen
timers,
music boxes, wind-up
toys and
clockwork radios.