Parts of a Watch Movement – Barrel, Train and Balance

All 17 parts on the diagram

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Bridges on 9

Crown Turning it winds the mainspring; pulled out, it sets the hands.
Stem The shaft that joins the crown to the winding and setting gears.
Pillar plate The plate that forms the foundation of the movement.
Bridge A bar screwed to the plate; the wheels turn between the two.
Jewels Hard stones used as bearings to cut friction and wear.
Ratchet wheel It turns the barrel arbor to wind the mainspring.
Click The pawl that stops the ratchet wheel from turning back.
Balance cock The bridge that holds the upper balance jewels.
Regulator A pointer moved to make the watch run faster or slower.

Bridges off 8

Mainspring barrel The round box that houses the mainspring; its teeth drive the train.
Center wheel It turns once an hour and carries the minute hand.
Third wheel It carries the power from the center wheel to the fourth wheel.
Fourth wheel It turns once a minute and carries the second hand.
Escape wheel The last wheel of the train, released one tooth at a time.
Pallet fork Rocks to and fro, locking the escape wheel and pushing the balance.
Balance wheel It swings back and forth at a steady rate to keep time.
Hairspring The fine spiral spring that swings the balance back each time.

How this list was compiled: Every name checked on 2026-09-30, a name kept only where two independent sources use it. (1) US War Department, TM 9-1575, Ordnance Maintenance: Wrist Watches, Pocket Watches, Stop Watches, and Clocks (1945), https://archive.org/details/TM9-1575, read in full: its functional description (power assembly, train, escapement, balance and hairspring, winding and setting, jewels) and its summary of timepiece terms give every name asked here. (2) Wikipedia, text only, read the same day: Mechanical watch, https://en.wikipedia.org/wiki/Mechanical_watch (mainspring barrel, center, third and fourth wheels, escape wheel, balance wheel, regulator, crown, stem, ratchet wheel and click, jewels); Movement (clockwork), https://en.wikipedia.org/wiki/Movement_(clockwork) (bridges, balance cock); Balance wheel, https://en.wikipedia.org/wiki/Balance_wheel (balance spring or hairspring); Lever escapement, https://en.wikipedia.org/wiki/Lever_escapement, and Wheel train, https://en.wikipedia.org/wiki/Wheel_train (pallet fork, the click as the pawl of the ratchet). (3) Paul N. Hasluck, The Watch Jobber's Handybook (1889), https://archive.org/details/cu31924031263134, read in full, for pillar plate, balance-cock, regulator, ratchet wheel and click. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; no maker's movement, nothing traced. Licence: own work

How it works

The parts of a watch movement sit on one round plate. The first drawing shows the back with its bridges on. The second lifts them off to show the barrel, the wheels and the balance.

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The back, bridges on

Numbers 1 to 9. The crown and stem stick out at the side. Two bridges cover most of the pillar plate, with jewels where the wheels turn. The ratchet wheel and its click sit on the upper bridge, and the balance cock carries the regulator.

Bridges off: the train

Numbers 10 to 17 follow the power. The mainspring barrel drives the center wheel, then the third, fourth and escape wheels. The pallet fork joins the escape wheel to the balance wheel, which the hairspring swings back.

The wheels overlap in the drawing because in a watch they sit at different heights.
A watch's jewel count is the number of these bearings in its movement.

Questions and answers

What are the internal parts of a watch?

A mainspring in its barrel, a train of wheels (center, third, fourth and escape), a pallet fork, and a balance wheel with its hairspring. They turn between a pillar plate and bridges. The crown and stem wind the mainspring and set the hands.

What does the balance wheel do in a watch?

It swings back and forth at a steady rate, turned back each time by the hairspring. Each swing lets the pallet fork release one tooth of the escape wheel, so the wheels and the hands move on in even steps.

What are the jewels in a watch movement for?

They are bearings. Hard stones such as sapphire and ruby sit where the pivots of the wheels and the balance turn, in place of metal on metal. That cuts friction and wear, so the watch keeps better time for longer.

How is a watch movement different from a clock movement?

A pendulum clock is timed by its pendulum. A watch is carried about, so it is timed by a balance wheel and hairspring instead. Both have a wheel train and an escape wheel between the power and the part that keeps time.