Pocket Watch Movement Parts — Illustrated Reference

The mechanical pocket watch contains between 100 and 300 individual components, each with a specific name and function. This illustrated reference covers the complete set of movement parts found in a typical lever-escapement pocket watch — from the mainspring barrel that stores the energy, through the gear train that transmits it, to the escapement and balance that regulate its release.

The four charts below show every significant part with its name and drawn illustration. A full alphabetical description of each part follows. For a numbered diagram showing where each part sits in an assembled movement, see the Pocket Watch Parts Diagram.

Parts Charts

Parts Reference — Group by Group

The following table describes every part shown in the charts above, grouped by the assembly it belongs to. Where a part has alternative names commonly used by watchmakers or in older English horological literature, these are noted.

The Mainspring Barrel

The mainspring barrel is a cylindrical drum that contains the coiled mainspring. As the spring uncoils, the barrel rotates and drives the going train. It is the fundamental energy store of the watch.

Part	Function
Barrel	The cylindrical drum containing the mainspring. Its toothed outer rim meshes with the centre wheel pinion to drive the train. The barrel lid snaps into a groove around the rim.
Mainspring	A coiled strip of hardened and tempered steel, typically 25–40cm long when uncoiled. Stores energy when wound; releases it progressively as it uncoils. The outer end hooks to the barrel wall; the inner end to the barrel arbor.
Barrel arbor	The central spindle of the barrel, to which the inner end of the mainspring is attached. The arbor is squared at one end to receive the winding key or crown wheel drive.

The Winding Train (Keyless Work)

In a keyless-wind watch (from c.1870 onward), turning the crown winds the mainspring through a series of small wheels and levers. In key-wind watches, the key engages the barrel arbor directly.

Part	Function
Stem	The winding and setting shaft — the axle on which the crown sits. Pulling the stem out one position engages the setting mechanism; in the normal position it drives the winding train.
Female winding stem	A tubular stem used in some movements where the stem is in two sections joined end-to-end. Allows the crown to be detached without removing the movement.
Crown wheel	The first wheel driven by the stem in the winding train. Not to be confused with the crown wheel of the verge escapement — in keyless-wind movements this is a small bevel-toothed wheel meshing with the winding wheel.
Castle wheel	A wheel with axial (upright) teeth around its rim, resembling castle battlements. In the setting position it engages the setting mechanism; in the winding position it drives the winding train.
Winding wheel	Transmits rotation from the crown wheel to the ratchet wheel, winding the mainspring.
Winding wheel bushing	A small sleeve or pipe that provides the pivot hole for the winding wheel arbor, allowing it to be replaced independently of the plate.
Intermediate wheel	An additional wheel in the winding or setting train, used to bridge a gap between other wheels or to reverse the direction of rotation.
Ratchet wheel	A toothed wheel on the barrel arbor that can only rotate in one direction — the winding direction — due to the action of the click. Allows the mainspring to be wound without it unwinding when the key or crown is released.
Click	A spring-loaded pawl that engages the teeth of the ratchet wheel, preventing it from rotating backwards (which would unwind the mainspring). Clicks on every tooth during winding; locks against a tooth when winding stops.
Click spring	The small spring that keeps the click pressed against the ratchet wheel teeth.
Return bar	Part of the setting mechanism. When the stem is pulled out, the return bar moves to engage the setting train and disengage the winding train, allowing the hands to be set.
Pull-out spring	The spring that holds the stem in its normal (winding) position. Pulling the crown out against this spring moves the stem to the setting position.
Check spring	Prevents accidental movement of the stem between winding and setting positions, ensuring positive engagement of each.
Return spring	A small spring that returns a lever or wheel to its rest position after it has been displaced.

The Going Train

The going train transmits power from the mainspring barrel to the escapement. Each successive wheel turns faster than the one before; the fourth wheel makes one revolution per minute.

Part	Function
Centre wheel	The first wheel of the going train. Meshes with the barrel. Its arbor carries the cannon pinion and minute hand. Makes one revolution per hour.
Cannon pinion	A small toothed cylinder (pinion) friction-fitted to the centre wheel arbor. Drives the motion work (minute and hour wheels) and carries the minute hand. The friction fit allows the hands to be set without stopping the movement.
Third wheel	The second wheel of the going train, driven by the centre wheel pinion. An intermediate wheel — no hand is carried on it.
Fourth wheel	The third wheel of the going train. Its arbor carries the seconds hand. Makes exactly one revolution per minute.
Minute wheel	Part of the motion work (on the dial side of the movement). Meshes with the cannon pinion and drives the hour wheel via a pinion. Rotates once per hour.
Hour wheel	Driven by the minute wheel pinion. Carries the hour hand. Makes one revolution per twelve hours.

The Escapement

The escapement controls the rate at which the going train runs — releasing it one tooth at a time while receiving energy to keep the balance oscillating. These parts are for the lever escapement, used in virtually all quality pocket watches from c.1800 onward.

Part	Function
Escape wheel	The final wheel of the going train. Its club-shaped teeth alternately lock against and receive impulse from the pallet stones. Advances one tooth per beat of the balance.
Pallet fork (anchor)	A pivoted lever, shaped like a ship's anchor, with two pallet stones set into its arms. Driven back and forth by impulse from the balance roller jewel, it alternately locks and unlocks the escape wheel. Also called the lever or anchor.
Anchor arbor	The pivot staff of the pallet fork, on which it rocks back and forth.
Pallet stone — entry	The pallet stone that receives the first contact from each escape wheel tooth as the tooth enters the pallet fork. Made of synthetic ruby or garnet, polished to a precise angle.
Pallet stone — exit	The pallet stone that releases the escape wheel tooth on the other beat. Its geometry determines the amount of impulse and the draw angle that keeps the lever safely in its locked position.

The Balance and Hairspring

The balance wheel oscillates back and forth under the control of the hairspring, providing the regular timekeeping interval. Temperature compensation, adjustment, and the form of the hairspring are the primary determinants of a movement's accuracy.

Part	Function
Balance staff	The axle of the balance wheel, running in jewelled pivot holes in the upper and lower balance cock/plate. The roller table is press-fitted to the staff.
Balance with arbor	The balance wheel as fitted to its arbor/staff before the roller is added — the intermediate assembly stage.
Balance with staff	The complete balance wheel assembly including staff but without the roller table.
Bi-metallic balance	A compensation balance with a split rim of two metals (typically brass outer, steel inner). Temperature changes cause the rim arms to flex, altering the effective moment of inertia and compensating for the hairspring's temperature coefficient. Required by railroad standards.
Complete balance with Breguet overcoil	The fully assembled balance — wheel, staff, roller table, and hairspring with Breguet overcoil (the outer coil elevated above the plane of the spring). The overcoil improves isochronism.
Flat hairspring with roller and block	The simpler hairspring form — a flat Archimedean spiral — assembled with the roller table and collet block. Used in lower and medium grades.
Breguet hairspring	A hairspring whose outer coil is raised above the plane of the others (the overcoil), terminating in a precisely calculated curve. Improves isochronism by making the oscillating period more independent of amplitude. Marks a higher-grade movement.
Roller table	A disc press-fitted to the balance staff, carrying the impulse roller jewel. Receives the impulse from the pallet fork and transmits it to the balance on each beat.
Roller jewel	A small synthetic ruby peg set into the roller table. Engages the notch in the pallet fork lever, receiving the impulse and locking the pallet fork safely between beats.
Regulator	The index or curb-pin assembly that controls the effective length of the hairspring, allowing rate adjustment. Moved toward F (fast) or S (slow). High grades use a micrometric regulator with fine-pitch adjustment screw.
Regulator for flat hairspring	The standard index regulator used with a flat hairspring — a curved arm with two pins (curb pins) between which the outer coil of the hairspring passes.
Regulator for Breguet hairspring	A modified regulator designed to work with the elevated outer coil of a Breguet overcoil spring without distorting it.
Lower cap jewel plate	The lower end-stone jewel assembly — a flat ruby disc that limits end-shake of the balance staff pivot and reduces wear at the tip.
Upper cap jewel plate	The upper end-stone jewel, set in the balance cock above the balance wheel. Together with the lower cap jewel, it completes the balance staff pivot support.

Screws

A standard pocket watch movement contains twelve or more different screw types, each designed for a specific function. Using the wrong screw — even one that fits — can damage threads, crush jewel settings, or prevent correct function.

Screw	Location & Function
Movement screw	General plate-to-plate screws securing bridges and cocks to the main plate. Typically blued steel on quality movements.
Bridge screw	Secures train bridges to the main plate. Usually slightly larger than movement screws.
Pull-out screw	Secures the pull-out spring or related lever in the setting mechanism.
Winding ratchet wheel screw	Secures the ratchet wheel to the barrel arbor. Must be correctly torqued — too tight distorts the arbor; too loose allows slipping.
Ratchet wheel screw	Variant of the above; some movements use a different screw form for the click ratchet.
Winding wheel screw	Secures the winding wheel to its arbor in the keyless work.
Hand-setting lever screw	Secures the setting lever or return bar in the keyless work.
Pull-out screw for return bar	A modified pull-out screw used to retain the return bar assembly.
Setting lever spring screw	Secures the spring that tensions the setting lever.
Upper cap jewel screw	The small screw retaining the upper end-stone (cap jewel) in the balance cock. Extreme care required — overtightening cracks the jewel setting.
Anchor screw	Secures the pallet fork (anchor) bridge to the main plate.
Lower cap jewel screw	Retains the lower end-stone in the lower balance jewel plate.
Hairspring block screw	The smallest screw in the movement — secures the hairspring collet or stud block to the balance cock. Requires a watchmaker's screwdriver of the correct width; a wrong-sized blade will slip and damage the cock.

For a visual overview of where each part sits within an assembled movement, see the Pocket Watch Parts Diagram with 55 labelled components. For the full alphabetical glossary see Pocket Watch Parts A–Z. For an explanation of how movement plate types differ, see Movement Types Explained.