Parts reference
Component Encyclopedia
Every mechanical watch and clock is built from a shared vocabulary of parts. Each component record here explains what the part is, what it does, how it works, how it evolved, its known variations, how to identify it on the bench, and how it typically fails — with cross-references into movements, complications and watch types that depend on it.
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PowerMainspringA long, coiled ribbon of tempered spring steel (or, from the mid-twentieth century, a cobalt-nickel alloy) that stores mechanical energy when wound.c. 1400s in clocks; miniaturised for portable watches from the early-to-mid 1500s
PowerBarrelA cylindrical drum, toothed on its outer circumference, that houses the mainspring.With the going barrel from the mid-1700s, though barrel-like spring boxes existed earlierPowerGoing BarrelA barrel-and-mainspring system that drives the going train directly, without an intermediate fusee to equalise torque.Used sporadically earlier, but standard in quality watchmaking from the second half of the 18th century onward as lever escapements matured
PowerFuseeA tapered, spirally grooved cone that equalises the torque delivered by a mainspring as it unwinds.Clock fusees recorded from the 15th century; adapted to portable watches from the 16th century
PowerFusee ChainA miniature articulated chain, similar in principle to a bicycle chain but on a much smaller scale, linking the mainspring barrel to the fusee cone.In use alongside fusees from at least the 16th century
PowerRatchet WheelA coarse-toothed wheel mounted on the mainspring barrel arbor, engaged by a click to permit winding in one direction only.With key-wound and later stem-wound mainspring barrels from at least the 17th–18th centuriesPowerCrown Wheel (Winding Train)A small toothed wheel in the winding train that transmits turning force from the winding pinion to the ratchet wheel (not to be confused with the crown wheel of the verge escapement).As part of winding-train arrangements from the earliest key-wound watches, later adapted for keyless winding in the 19th century
PowerClickA small, spring-loaded pawl that engages the ratchet wheel's teeth to enforce one-directional winding.Alongside ratchet-wheel winding systems from at least the 17th–18th centuriesPowerClick SpringA small flat or curved spring that presses the click into engagement with the ratchet wheel's teeth.Alongside click-and-ratchet winding assemblies from at least the 17th–18th centuriesTrainCentre WheelThe second wheel in the going train (after the barrel), usually running once per hour, from which the minute hand is normally driven via the motion works.Standard in going-train architecture since the earliest wheel-train watches and clocks
TrainThird WheelThe wheel positioned between the centre wheel and the fourth wheel in the going train.Standard in multi-wheel going trains since early wheel-train watches and clocksTrainFourth WheelThe train wheel that typically rotates once per minute and commonly carries the seconds hand.Standard once subsidiary seconds displays became common from the 18th century onwardEscapementEscape WheelThe last and most specialised wheel of the going train, shaped to interact with the escapement's locking and impulse elements.In some form since the earliest mechanical escapements (verge, from the medieval period); tooth geometry evolved substantially with the lever escapement from the 18th century
EscapementPallets / Pallet ForkIn a lever escapement, an assembly combining two jewelled pallet stones set in a steel fork, which alternately locks and releases the escape wheel while communicating impulse to the balance.The lever escapement is generally attributed to Thomas Mudge around the 1750s; refined and popularised through the 19th century
EscapementBalance WheelThe oscillating wheel-and-staff assembly that, together with the balance spring, forms a watch's timekeeping oscillator, analogous to a clock's pendulum.From the earliest verge watches of the 16th century, refined enormously with the balance spring's addition in the 1670sEscapementBalance Spring (Hairspring)A very fine, coiled spring, typically of specialist alloy, attached to the balance staff and to a fixed stud, that provides the restoring force for balance oscillation.Its application to watches is generally credited to the 1670s, associated with Robert Hooke's and Christiaan Huygens's competing claims
RegulationRegulatorAn adjustable index, typically a curb-pin carrier arm, that lets the effective free length of the balance spring be shortened or lengthened.Regulator indexes appear from the 18th century onward as balance-spring watches matured
Plates & finishingJewelsSmall bearings or functional stones, historically natural ruby and now synthetic sapphire or ruby, used at points of high friction and wear in a movement.Jewelling of watch movements is generally credited to the 1700s, associated with Nicolas Fatio de Duillier, Peter and Jacob Debaufre in EnglandPlates & finishingBearings / BushingsThe plain (non-jewelled) holes or inserted bushes in plates and bridges through which train and other arbors pivot.Since the earliest wheel-train mechanisms; separate replaceable bushings became common repair practice from at least the 18th–19th centuries onward
Plates & finishingBridgesIndividually shaped metal supports, fixed at both ends (or more), each carrying the upper pivot(s) of one or more train components.Bridge (or 'bar') construction is strongly associated with Swiss and French watchmaking from at least the 18th–19th centuries, contrasted with the English full-plate tradition
Plates & finishingPlatesThe main flat metal structures that sandwich and support the entire movement's train, escapement and other working parts.Since the earliest plate-and-pillar watch and clock movements of the 16th–17th centuries
Dial & handsCannon PinionA friction-fitted pinion mounted on the centre wheel arbor that carries the minute hand.With the development of separate motion (hand-setting) works, widespread from the 18th century onward
Dial & handsMinute WheelA wheel-and-pinion component in the motion works that connects the cannon pinion to the hour wheel.With separate motion works from the 18th century onward
Dial & handsHour WheelA larger, tube-mounted wheel that carries the hour hand and completes one revolution every twelve hours.With separate motion works from the 18th century onwardDial & handsMotion WorksThe collective name for the cannon pinion, minute wheel and hour wheel that together translate the going train's centre wheel rotation into correctly geared minute and hour hand display.Separate motion works able to be independently set became standard alongside developments in keyless winding and setting during the 18th and 19th centuries; earlier watches sometimes lacked independent hand-setting.Keyless workKeyless WorksThe system of levers, wheels and a sliding clutch (usually operated by pulling out the crown) that allows a watch to be wound and its hands set entirely via the crown, without a separate winding key.Early keyless mechanisms appeared from the mid-19th century, becoming near-universal in quality watchmaking by the late 19th and early 20th centuries
Keyless workStem (Winding Stem)A slender steel shaft that passes through the case pendant, connecting the external crown to the internal keyless works.With keyless works from the mid-to-late 19th century
Keyless workCrownThe external knurled knob, typically at the 3 o'clock edge of the case, used to wind the mainspring and set the time (and, on many watches, the date).With keyless works from the mid-to-late 19th century; earlier watches were wound and set by a separate key
Keyless workSetting LeverA small spring-loaded lever within the keyless works that pivots to slide the clutch between winding and setting positions.With keyless works from the mid-to-late 19th century
Dial & handsDialThe face of the watch, marked with hour and minute indications (numerals, indices, a chapter ring, or a combination), against which the hands display the time.Dials have existed since the earliest mechanical clocks and watches; painted, enamel and metal dials all appear from the 16th–17th centuries onward, with printed and applied-marker dials becoming dominant from the 19th–20th centuries.
Dial & handsHandsThe indicator pointers — typically hour, minute and often a seconds hand — mounted on the motion works' arbors above the dial.Single (hour) hands were standard in early clocks and watches; minute hands became common from the late 17th century as escapements grew accurate enough to justify them, and seconds hands became widespread with higher-precision movements from the 18th–19th centuries onward.
CaseCaseThe external housing that protects the movement, dial and hands from dust, moisture and physical damage.Watch cases exist from the earliest portable watches of the 16th century; water-resistant and screw-back/screw-bezel cases developed substantially in the 20th century.
CaseCase BackThe rear cover of the watch case, closing off the movement from behind.Present on watch cases from their earliest portable form in the 16th century; screw-down and snap-fit backs developed through the 19th–20th centuries.
CaseCase HingesThe pivoted joints that allow a hunter-case cover, or a hinged case back or bezel, to swing open and closed.Since hunter-cased and hinged-back pocket watches of the 17th–19th centuriesCaseDust Cover (Cuvette)An inner metal cover, also called a cuvette, fitted over the movement beneath the outer case back, chiefly in pocket watches.Common in pocket watches from at least the 18th–19th centuries onward, particularly in higher-grade and open-face watches
CaseBezelThe ring surrounding and retaining the crystal at the front of the case.Present in some form on watch cases since their earliest development; rotating functional bezels developed prominently in 20th-century tool and dive watches.
CaseCrystal (Glass)The transparent cover, historically glass and today also acrylic (plastic) or synthetic sapphire, that protects the dial and hands while allowing them to be read.Mineral glass crystals appear from the earliest cased pocket watches; acrylic (plastic) crystals became common mid-20th century, and synthetic sapphire crystals became widespread in quality watchmaking from the late 20th century onward.
CasePendantThe small projecting tube at the case edge (traditionally the top of a pocket watch) through which the stem passes, and to which a bow or crown attaches.Present on watch cases from their earliest development as the means of suspension and later of stem entry
CaseBowThe ring or loop, hinged to the pendant, from which a pocket watch is suspended by a chain, fob, or ribbon.Present on pocket watches from their earliest developmentDial & handsChapter RingThe graduated ring on a dial marked with the hour (and often minute) divisions against which the hands indicate the time.Chapter rings appear on clock and watch dials from the earliest examples, with Roman numeral chapter rings especially associated with 17th–19th century clock and watch dials
Dial & handsSubdialA smaller, secondary dial set into the main dial, displaying an auxiliary indication such as running (small) seconds, a chronograph totaliser, or a power-reserve indicator.Small seconds subdials appear from the era when seconds indication became common, from the 18th–19th centuries; chronograph and multi-register subdials became widespread with complicated wristwatch movements through the 20th centuryPlates & finishingBlued ScrewsSmall movement screws heat-treated to a deep blue colour, combining a hardened temper with a decorative, corrosion-resistant surface oxide layer.Screw bluing as a finishing technique is documented from at least the 18th century in fine watchmakingPlates & finishingDecorative FinishingThe collective term for ornamental surface treatments applied to movement plates, bridges and components — including Geneva stripes (côtes de Genève), perlage, black polishing, bevelling (anglage) and engine-turning (guilloché).Decorative movement finishing techniques are documented in fine watchmaking from at least the 18th–19th centuries, closely associated with Swiss and French haute horlogerie traditions
Plates & finishingPivotsThe finely turned, reduced-diameter ends of an arbor that run in bearings, jewels or bushings.Since the earliest geared clock and watch mechanisms required rotating arbors
Plates & finishingScrewsThe small threaded fasteners used throughout a movement to secure bridges, springs, jewels, and other components to the plates.Screwed construction became standard in watchmaking from the 17th–18th centuries onward, progressively displacing earlier friction and pinned fitsPlates & finishingPinsSmall, unthreaded steel rods used to locate, retain, or transmit force between components without the mass or complexity of a screw.Pinned construction predates screwed construction in early clock and watch making and remains in use for specific purposes throughout horological historyTrainPinionsSmall-diameter, few-toothed ('leaved') gears, typically the driven member in a wheel-and-pinion pair within the going train.Since the earliest geared mechanical clock and watch trainsPowerStopwork (Geneva Stop-Work)A limiting mechanism, most often a Maltese-cross-and-finger arrangement, fitted to the barrel to restrict the usable number of mainspring turns.In use on fine watches and clocks from at least the 17th–18th centuries, alongside fusee and going-barrel practice
PowerMaltese CrossA five-pointed star-shaped wheel, one point of which is solid rather than slotted, used as the indexing element of Geneva-style stopwork.Associated with fine watch and clock stopwork from at least the 17th–18th centuriesPowerMainspring HookThe small formed hook, tab, or slot at the outer end of a mainspring that anchors it to the inside of the barrel wall.Present in mainspring-and-barrel construction since the earliest going barrels and fusee barrelsPowerBarrel ArborThe central steel shaft running through the mainspring barrel, onto which the mainspring's inner coil is anchored.Present in barrel construction since the earliest key-wound and fusee watchesKeyless workClutch Wheel (Castle Wheel)A splined wheel, also called the castle wheel, that slides along the winding stem's square section and can be shifted between winding and hand-setting positions.With the development of keyless (stem-wind, stem-set) winding systems from the mid-19th centuryKeyless workYokeA forked lever within the keyless works that engages a groove on the stem and shifts the clutch wheel between its winding and setting positions.With keyless works from the mid-to-late 19th century onwardKeyless workSetting WheelsA small train of intermediate wheels within the keyless works that carries drive from the clutch wheel to the minute wheel when the crown is used to set the hands.With keyless works from the mid-to-late 19th century onwardEscapementRoller TableA disc mounted on the balance staff that carries the impulse jewel (and, on double-roller designs, a separate safety roller) for exchanging impulse with the pallet fork.With the development of the detached lever escapement from the late 18th century onwardEscapementImpulse Jewel (Roller Jewel)A small pin, usually of synthetic ruby or sapphire, projecting from the roller table and engaging the pallet fork's slot.With the lever escapement's development from the late 18th century, jewel material becoming standard through the 19th and 20th centuriesEscapementBanking PinsA pair of fixed pins (or an adjustable banking-to-drop mechanism) that limit the pallet fork's swing to a small, precise arc.With the development of the lever escapement from the late 18th centuryEscapementGuard PinA small pin projecting from the pallet fork, positioned to run close to the safety roller and prevent the fork from moving into the path of the balance when unlocked.With the development of double-roller and single-roller safety systems in the lever escapement, from the 19th centuryEscapementSafety RollerA small disc, distinct from the main roller table, mounted lower on the balance staff in a double-roller escapement, engaged by the pallet fork's guard pin for shock safety.With the development of double-roller lever escapements, a refinement of the earlier single-roller safety system, through the 19th centuryRegulationCurb PinOne of a pair of small pins, mounted on the regulator index, between which the outer coil of the balance spring (hairspring) passes.With the development of balance-spring regulation from the late 17th century onward
RegulationPendulum RodThe rigid or compensating rod suspending the pendulum bob, whose effective length governs the clock's rate.With the pendulum clock's introduction, associated with Christiaan Huygens's application of the pendulum to clockwork in 1656–1657RegulationPendulum BobThe weighted mass at the bottom of a pendulum rod, providing most of the pendulum's inertia.With the pendulum clock's introduction from the mid-17th centuryRegulationSuspension SpringA thin, flexible strip of spring steel from which the pendulum is hung, allowing it to swing freely while maintaining a fixed pivot axis.Associated with pendulum clock development from the mid-to-late 17th century, refined through the 18th and 19th centuries in precision clocksRegulationCrutchA forked or pinned arm connecting the pallet arbor of a clock's escapement to the pendulum rod.With anchor-escapement pendulum clocks from the late 17th century onwardEscapementAnchor (Verge-Successor) EscapementA pendulum-clock escapement in which an anchor-shaped pallet, rocked by the pendulum via the crutch, alternately locks and releases an escape wheel.Introduced in the second half of the 17th century, superseding the earlier verge escapement in pendulum clocks; the recoil form later refined into the deadbeat escapementTrainCount Wheel (Locking Plate)A notched wheel in a clock's striking train whose notches, of varying spacing, determine how many blows are struck at each hour.In striking clocks from at least the medieval period, an early solution to the problem of counting strikes correctly, well before the rack-and-snail alternativeTrainRack and SnailA self-correcting hour-striking mechanism in which a toothed rack falls against a stepped cam (the snail) mounted on the hour wheel to set the correct number of strikes.Developed in the late 17th century as an improvement on count-wheel striking, and often associated with Edward Barlow's rack-striking work of that period, though attribution among several contemporaries is debated in the literatureCaseCuvetteAn inner protective cover, usually hinged or snap-fitted, fitted over the movement inside a pocket watch case, beneath the outer case back.Common in pocket watch case construction from at least the 18th–19th centuriesCaseSpring BarA small spring-loaded rod, telescoping under internal spring pressure, used to attach a strap or bracelet to the lugs of a wristwatch case.With the development of wristwatch case-and-strap attachment from the early 20th century onwardCaseLugOne of a pair (or two pairs) of projections extending from a wristwatch case, drilled or notched to accept the spring bars that attach a strap or bracelet.With the emergence of purpose-built wristwatch cases in the early 20th century, evolving from wire-lug conversions of earlier pocket-watch-style casesMethod
How to use the component encyclopedia
1. Start from a group
Power, train, escapement, regulation, keyless work, plates & finishing, dial & hands, and case each gather parts that work together. Filtering by group is the fastest way to see a subsystem end to end.
2. Read the mechanics, not just the name
Every record explains how the part works in context — how it meshes, transmits force, or resists wear — so you can reason about a movement you're looking at rather than just labelling it.
3. Follow the related links
Components link to the other parts they depend on or drive, and out to movements and watch types where relevant, so you can trace a full mechanism across the archive.