Very hard stone (formerly a ruby, today a rock crystal) that resists wear; the rotation axle of a wheel rests on it.
escape wheel
Last wheel of the gear train with special teeth that causes the watch to operate regularly and continuously; it controls the movement of the other wheels.
hairspring
Flat spiral spring that causes the wheels of a watch to move over a certain period of time.
center wheel
Wheel that is connected to the hands and causes them to rotate on the dial.
ratchet wheel
Toothed wheel having only one direction of rotation; it is kept in place by the click.
click
Small lever that is engaged between the ratchet-wheel teeth and prevents it from rotating counter to its normal direction.
winder
Part that rewinds the mechanism, consisting of a series of wheels.
third wheel
Wheel that receives energy from the fourth wheel and drives the center wheel.
