stem – the shaft that connects to the movement’s winding mechanism, the crown is fitted to the opposite end.

bridge – attached to the bottom plate to hold components in place. Fixed to the main plate to form the frame of a watch.

shock absorbers – spring devices in balance wheel bearings that divert shocks away from the fragile pivot to the sturdier parts of the balance staff. The springs allow the balance wheel to return to its original position aftershocks.

rotor – part of an automatic watch that winds the mainspring. A flat piece of metal swivels on a pivot with the motion of the wrist. Its rotation continually winds the mainspring of the watch. It turns freely in both directions and uses the force of gravity to wind the mainspring.

pinion – small toothed wheel usually made of steel with a small number of teeth that mesh with gear train wheels.

pallets – typically made of synthetic rubies, meshes with the teeth of the escapement wheel and transmits an impulse to the balance.

balance spring – (same as “hairspring”) is one of the most important components of a mechanical timepiece. The balance spring is a fine spiral torsion used in mechanical wristwatches to control the rate of oscillation of the balance wheel, and thus the rate of the movement of the hands and accuracy of the timepiece. It is an integral part of the balance wheel because it reverses the direction of the balance wheel causing it to oscillate to-and-fro (back-and-forth). Considered the heart of a mechanical timepiece.

balance wheel – regulating organ of the watch, vibrating on a spiral hairspring. Lengthening and shortening of the balance spring make the balance wheel go faster or slower to advance or retard the watch.

barrel – a cylindrical box containing the mainspring of a watch. The toothed rim of the barrel drives the train.

bezel – the ring around the top of the crystal. Generally, hold the glass or crystal in place. A rotating ratchet bezel moves in some watches as part of a complication. Rotating bezels either rotate clockwise (uni-directional) or both counter-clockwise and clockwise (bi-directional) to assist in calculations.

crown – knob used to wind a mechanical watch and to set the time and/or calendar of a watch.

dial – face of the watch that generally displays hours, minutes, and seconds.

mainplate – (or “baseplate”) the plate on which all other parts of a watch movement are mounted to the metal piece that holds up the bridge and other parts of the movement. The bottom side is the dial side the top side is the bridge side. supports the bridges, which are often on the top of the plate, the movement, the dial, and the holes where the jewels are inserted.

mainspring – this spring’s tension controls the amount of energy transmitted to the measurement. Hooked to the barrel and arbor, when it is tensed it releases energy. The driving flat-coiled spring of a watch contained in the barrel or barrels that supplies power. This is what is wound, by hand or via an oscillating weight, and then unwound to power a watch.

flange – a ring that separates the crystal from the dial.

escapement – mechanism made up of the escapement wheel, lever, and discharging roller, which act to control the wheel movement and to provide pulses to pallets and thus the balance. Converts the energy of the mainspring into equal units of time. The escapement controls the amount of power released from the mainspring. The regularity is controlled by the balance and its spring. The escapement controls the rotation of the wheels and thus the motion of the hands. It is fitted at the end of the gear train and is designed to interrupt the movement of the wheels at regular intervals. (The escapement is the source of the ticking sound in watches and clocks.)

watch hands – watches generally have three hands for seconds, minutes, and hours. They come in many different shapes: Pear, Breguet, Baton, Arrow, Skeleton, Luminous, Alpha, Dauphine and more.

jewels – (also called “rubies”) synthetic sapphires or rubies that are used in a watch movement to reduce friction. They help maintain the watch’s lubrication. More jewels do not necessarily denote higher quality.

lug – (same as “horn”) part of case where bracelet or strap is attached.

spring bar – a spring-loaded metal bar mounted between the case lugs used to attach the strap or bracelet.

arbor – the shafts that the wheels and pinions are mounted on.

sapphire crystal – synthetic corundum crystal with a hardness second only to a diamond. Transparent sapphire is used for a scratchproof watch glass. Made of crystallizing aluminum oxide at very high temperatures. Chemically the same as natural sapphire, but colorless. It is hard and brittle so it shatters easier than plexiglass or mineral glass. 9 on a Mohs scale, a diamond is 10.

fusee – grooved pulley that equalizes the mainspring by controlling its winding or unwinding.

gasket – most water resistant watches are equipped with gaskets to seal the caseback, crystal, and crown from the water. Gaskets need to be checked every couple of years to maintain water resistance.