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 centuries
PowerCrown 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 centuries
PowerClick 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 centuries
TrainCentre 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 1670s
EscapementBalance 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 England
Plates & 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 centuries
CaseDust 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 development
Dial & 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 century
Plates & 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 watchmaking
Plates & 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 history
TrainPinionsSmall-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 trains
PowerStopwork (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 centuries
PowerMainspring 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 barrels
PowerBarrel 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 watches
Keyless 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 century
Keyless 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 onward
Keyless 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 onward
EscapementRoller 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 onward
EscapementImpulse 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 centuries
EscapementBanking 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 century
EscapementGuard 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 century
EscapementSafety 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 century
RegulationCurb 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
RegulationBalance Screws (Timing Screws)Small screws set into the rim of a balance wheel, used historically to adjust the balance's effective mass distribution (poise and timing) and, in compensation balances, temperature response.With screwed balances from the 18th century onward, particularly associated with bimetallic compensation balances of the 19th century
RegulationHairspring StudA small fixed post that anchors the outer end of the balance spring (hairspring) to the balance cock or stud carrier.Present in balance-spring construction since spiral balance springs were introduced in the late 17th century
RegulationRegulator BootA small sliding piece on some regulator indexes that supports the balance spring near the curb pins, reducing distortion of the coil as the index is moved.As a refinement to simple curb-pin indexes, seen in higher-grade watch and chronometer regulation from the 18th–19th centuries 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 onward
EscapementAnchor (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 escapement
TrainCount 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 literature
CaseCuvetteAn 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 centuries
CaseSpring 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 onward
CaseLugOne 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 cases
EscapementBalance StaffThe hardened steel arbor running through the centre of the balance wheel, carrying the hairspring collet, the roller table, and the pivots on which the whole balance assembly turns.Present in essentially every balance-wheel escapement since the balance's introduction; the modern hardened, precisely turned and pivoted staff is a product of continuous refinement through the 18th–20th centuries
EscapementBalance CockA single-footed bridge, screwed to the main plate, that carries the upper pivot bearing of the balance staff and, usually, the regulator index.Balance cocks of recognisable form appear from the early era of the balance-and-hairspring escapement in the 17th century onward, becoming a favoured surface for engraving and piercing in decorative watchmaking
EscapementPallet Stones (Pallet Jewels)The two hard synthetic ruby (or, historically, natural ruby) stones set into the arms of the pallet fork, whose faces actually lock and unlock the escape wheel.Jewelled pallets became standard alongside general jewelling of quality watch movements from the 18th–19th centuries onward; earlier and cheaper work used steel palletsTrainCentre-Seconds PinionA pinion (and its associated friction-driven or indirectly geared wheel) that carries a seconds hand mounted concentrically with the hour and minute hands at the centre of the dial.Direct centre-seconds arrangements exist from early clockwork; friction-driven indirect centre-seconds became widespread in wristwatches through the mid-20th century as sweep-seconds displays became fashionable
PowerMainspring Bridle (Slipping Bridle)A separate outer band, riveted or otherwise attached to the outer coil of a mainspring, designed to grip the inside of the barrel wall only up to a controlled maximum torque.Slipping bridle mainsprings became a common feature of automatic (self-winding) wristwatches from the mid-20th century onward, where the mainspring can otherwise be wound repeatedly and continuously by wrist motion
RegulationBreguet OvercoilA raised, curved terminal section of a balance spring, bent up out of the plane of the flat coils and curved back over them, named after Abraham-Louis Breguet, who is credited with introducing it.Attributed to Abraham-Louis Breguet in the early 19th century; the theoretical basis for optimal overcoil geometry was later analysed mathematically, notably associated with work carried out by Moritz Immanuel Phillips
RegulationHairspring ColletA small collar, split or friction-fitted, that clamps the inner end of the balance (hair)spring to the balance staff.A necessary companion component wherever a balance spring has been fitted to a balance staff, since the earliest application of the balance spring in the late 17th century
EscapementShock-Protection SystemA spring-mounted jewel bearing assembly at the balance staff's pivots, designed to cushion the staff against impact and allow it to move slightly off-axis under shock rather than snapping.Practical shock-protection systems became widely available from the second quarter of the 20th century, with several proprietary designs (widely associated with the trade name Incabloc, among other systems) becoming common through the mid-20th century onward
Dial & handsDial WasherA thin washer, typically of brass or fibre, fitted over the centre arbor or cannon pinion post beneath the motion works to take up end-shake and maintain correct spacing.A routine fitting wherever motion works with hand-setting have been assembled, in use since separate motion works became standard in the 18th–19th centuries
Dial & handsDial FeetSmall pins or posts projecting from the underside of a dial, used to locate and secure the dial to the movement's pillar plate.A standard dial-fixing method in essentially all watch and clock dials with a separate movement, in use throughout the history of dial-and-movement construction
Plates & finishingJewel Settings (Rubbed-In vs Friction-Set)The method by which a jewel bearing is fixed into a plate or bridge: either burnished directly into a recess in the metal ('rubbed-in') or held within a separate metal collar ('chaton') that is itself friction-fitted or screwed into place.Rubbed-in settings are the older and simpler method, used since jewelling became common practice from the 18th–19th centuries; separately mounted chaton settings, particularly gold chatons secured by tiny screws, are associated with higher-grade watchmaking of the 19th and 20th centuries
Keyless workKeyless Works Cover PlateA shaped plate, usually held by one or two screws, fitted over the keyless works on the dial side to retain and protect the clutch wheel, yoke, setting lever and associated components.A standard fitting wherever keyless works have been used, from the development of stem-wind, stem-set systems in the mid-to-late 19th century onward
CaseMovement Ring (Casing Ring)A ring, often of brass or another soft metal, fitted around the outer edge of a movement to take up the difference between the movement's diameter and a larger case, and to provide a secure seat within the case.In use wherever standardised movement calibres have needed to be fitted into cases of varying size, common practice through the 20th century in both pocket watch and wristwatch manufacture
CaseCase ScrewsSmall screws used to secure the movement within the case, and, in some case designs, to hold the case back or bezel closed.Case-clamp and case screws are a longstanding standard fitting wherever movements have been secured within cases rather than simply pressure-fitted
Keyless workHacking Lever (Hack Mechanism)A small lever, engaged when the crown is pulled to the hand-setting position, that presses against the balance wheel's rim (or, in some designs, the seconds train) to stop it running while the time is set.Hacking mechanisms became a widespread and often explicitly advertised feature of military and precision wristwatches from the mid-20th century onward, where precise time synchronisation between instruments and personnel was operationally important
EscapementVerge (Verge Escapement Assembly)The earliest widely used mechanical escapement, comprising a crown-shaped escape wheel and a vertical staff (the verge) carrying two flag-shaped pallets set at roughly a right angle to each other.Verge escapements are recorded in European clocks from at least the fourteenth century and were adapted for portable watches from the sixteenth century, remaining in common use into the early nineteenth century in cheaper work.
EscapementCylinder EscapementA frictional-rest escapement in which a hollow steel or ruby cylinder, cut away over part of its circumference, forms part of the balance staff and is alternately entered and released by the teeth of a specially shaped escape wheel.Devised in England around the start of the eighteenth century and associated with George Graham's development work, later refined and produced in quantity (including with ruby cylinders) particularly in Switzerland through the eighteenth and nineteenth centuries.
EscapementDuplex EscapementA frictional-rest escapement using an escape wheel with two sets of teeth — long locking teeth and short impulse teeth — acting on a single roller carried on the balance staff.Developed in England in the eighteenth century (commonly associated with work attributed to Jean-Baptiste Dutertre and Thomas Tyrer, with refinement credited to various makers); most strongly associated with nineteenth-century American and English watchmaking, including some railroad-grade watches before the lever's dominance.
EscapementDetent (Chronometer) EscapementA fully detached escapement, used chiefly in marine chronometers and some precision pocket watches, in which the balance is left completely free of the escapement for almost the whole of its swing and receives impulse directly from the escape wheel only once per full oscillation.Developed through the eighteenth century by several makers (including Pierre Le Roy, Thomas Earnshaw and John Arnold, whose respective contributions and priority are debated in the literature), becoming the standard marine chronometer escapement by the early nineteenth century.
PowerRotor (Automatic Winding Weight)A pivoted, semicircular or near-circular weighted plate mounted over the movement that swings with the wearer's wrist motion, winding the mainspring without manual effort.Rotor-based automatic winding is generally traced to designs by John Harwood in the 1920s (a bumper/oscillating-weight system with a limited swing arc), with the modern full-rotor form widely credited to Rolex's 1930s 'Perpetual' system that allowed the weight to swing through a complete 360-degree circle.
PowerReversing WheelsA small pair (or set) of interacting wheels or pawls in a bidirectional automatic-winding train that convert rotor motion in either direction into a single, consistent winding direction at the ratchet wheel.Bidirectional winding systems using reversing wheels or pawls became widespread as automatic wristwatch calibres matured through the mid-twentieth century, improving on earlier unidirectional bumper and rotor systems.
PowerBumper (Oscillating) WeightAn early form of automatic-winding weight that swings through a limited arc, striking buffer springs at each end of its travel rather than rotating fully, historically associated with pioneering self-winding designs of the 1920s–1940s.Associated with John Harwood's automatic winding system patented in the 1920s, and used by several manufacturers before the full 360-degree rotor became the industry standard.
RegulationEndstone (Cap Jewel)A flat jewel (commonly synthetic ruby or sapphire) fitted over the end of a pivot hole to close its end and provide a smooth bearing surface against the flat end of a pivot.Cap jewels came into common use as jewelling became more sophisticated through the eighteenth and nineteenth centuries, becoming standard on the balance of quality watches and, later, widely used in industrial production.
CaseCrown Tube (Winding Stem Tube)A threaded metal tube fitted through the case band at the pendant, through which the winding stem passes to connect the crown to the movement.A necessary feature of keyless (crown-wound) watch cases from the later nineteenth century onward, with sealing refinements developing through the twentieth century alongside water-resistant case design.
CaseGasket (Case Seal)A ring or washer, generally of synthetic rubber or a similar elastomer (historically sometimes cork, felt or shellac-impregnated fibre in early attempts at sealing), compressed between case components to exclude moisture and dust.Early attempts at sealing watch cases against moisture date to the 1920s–1930s (contemporaneous with the first widely marketed water-resistant cases); modern synthetic rubber and later fluoroelastomer gaskets became standard through the mid-to-late twentieth century.Keyless workWinding PinionA small, splined or square-bored pinion at the inner end of the winding stem that slides along the stem and engages the keyless winding train when the crown is turned for winding.A necessary part of keyless (crown-wound, non-key) watches from their introduction and standardisation through the second half of the nineteenth century.
TrainGreat Wheel (Clock First Wheel)The first, largest wheel of a weight- or spring-driven clock's going train, mounted on the barrel or on the same arbor as the winding drum or mainspring barrel.Present in essentially all weight- and spring-driven clocks from the earliest mechanical clocks onward, the terminology itself long-established in English clockmaking practice.
PowerBarrel CoverThe thin removable lid that closes a mainspring barrel, snapped into a groove turned inside the rim of the barrel drum.With the enclosed spring barrel itself, which appears in the earliest spring-driven clocks and watches
PowerBarrel Arbor HookThe small raised hook (or, in some designs, a slot) on the central core of the barrel arbor that catches the eye pierced in the mainspring's inner coil.With the spring barrel; the same principle anchors the spring in clock barrels and watch barrels alike
TrainIntermediate WheelA wheel placed between two others to carry motion across a gap or to reverse its direction, without being part of the main ratio-setting train.As old as wheelwork itself; used throughout clock and watch trainsPlates & finishingMinute Wheel BridgeA small plate or cock on the dial side of the main plate that holds the minute wheel (and sometimes other motion-work or setting wheels) in place.With keyless work in twentieth-century calibres; earlier movements often retained the minute wheel by a stud or the dial
Keyless workSetting Lever SpringThe detent spring that holds the setting lever in each crown position (winding, date setting where fitted, and hand setting).With keyless winding and lever setting in the nineteenth century
RegulationStud CarrierThe fitting on the balance cock that holds the hairspring stud, in many modern movements as a movable carrier that can be turned around the balance axis.Fixed studs date from the earliest balance-spring watches; movable stud carriers became common in twentieth-century Swiss calibresEscapementPallet Arbor (Pallet Staff)The fine steel arbor on which the pallet fork is mounted, pivoting in jewels between the main plate and the pallet cock.With the lever escapement
EscapementEscape PinionThe small pinion on the escape-wheel arbor, driven by the fourth wheel.With wheel-train timekeepers
Keyless workDate JumperThe sprung lever that drops between the teeth of the date ring to position it exactly and hold it there between changes.With calendar watches; standard in date wristwatches from the mid-twentieth century
Dial & handsDate RingThe toothed ring (or disc) under the dial printed with the numerals 1 to 31, shown one at a time in a dial aperture.With date wristwatches of the mid-twentieth century; earlier calendar watches used hands on subsidiary dials
Dial & handsDay DiscA disc printed with the days of the week, shown in a dial aperture in day-date watches.With day-date wristwatches of the mid-twentieth century
Dial & handsMoonphase DiscA disc painted or printed with two moons, rotating behind a shaped aperture so that the visible moon waxes and wanes.In astronomical clocks and watches of the early modern period; common in calendar wristwatches
TrainChronograph Reset HammerThe pivoted steel lever, or set of levers, whose faces strike the heart cams on the chronograph arbors to return the hands to zero.With the return-to-zero chronograph using heart cams, from the mid-nineteenth century
TrainHeart CamA heart-shaped cam fixed on a chronograph arbor (and in some other mechanisms) which, when pressed by a hammer, turns to a fixed position.The return-to-zero heart is generally credited to Adolphe Nicole in the 1840s
TrainVertical ClutchA friction clutch mounted on the chronograph seconds arbor, in which a disc is pressed against a continuously turning wheel to start the chronograph.In series production from the late 1960s, notably in Seiko's 6139 automatic chronograph of 1969; now usual in many modern automatic chronographs
TrainMinute Counter JumperThe spring jumper that holds the chronograph's minute-counter wheel in position between steps, so the counter advances cleanly once per minute.With chronographs fitted with minute counters in the nineteenth century
TrainAlarm Hammer (Clock)The hammer in an alarm clock that vibrates rapidly against the bell when the alarm is released.With mass-produced alarm clocks of the nineteenth century, and in earlier alarm work in some form
RegulationSuspension Block (Chops)The block or pair of clamping plates (chops) that grips the top of a clock's pendulum suspension spring and hangs it from the back cock or bracket.With spring-suspended pendulums from the later seventeenth centuryRegulationCrutch PinThe pin (or fork) at the lower end of a clock's crutch that engages the pendulum rod.With the anchor escapement and long pendulum from the later seventeenth century
PowerClock Line and BarrelIn a weight-driven clock, the gut line, cord or steel cable wound on a grooved barrel (drum) attached to the great wheel, from which the driving weight hangs.With weight-driven clocks of the medieval period; gut line on grooved barrels is characteristic of English longcase and other domestic weight clocks
Dial & handsHand Collet (Clock)The small brass collet, usually domed, that holds a clock's minute hand on its arbor, retained by a taper pin through the arbor.With dial clocks of the early modern period
Dial & handsClock Dial PlateThe dial of a clock, either a brass plate with an applied chapter ring and spandrels or a painted iron (white) dial, fixed to the movement by dial feet.Brass dials from the seventeenth century; painted iron dials in British clocks from about the 1770s
CaseBell and Gong AssemblyThe sounding element struck by a clock's or repeating watch's hammer: a cast bell, a coiled wire gong, a straight rod gong or tubular bells.Bells from the first striking clocks; wire gongs in repeating watches from the late eighteenth century; coiled gongs in clocks from the nineteenth century
PowerRotor BearingThe bearing on which the oscillating weight (rotor) of a self-winding watch turns, either a plain bearing on a central post or a ball bearing.Plain-bearing rotors appear with the first rotor self-winders; the ball-bearing rotor was introduced by Eterna in 1948
Plates & finishingBalance BridgeA support for the balance fixed at both ends, spanning the balance, instead of the single-footed balance cock.In various high-grade and modern calibres; Rolex adopted a full balance bridge in its calibre 3135 family
RegulationMicrometric Regulator (Swan-Neck and Screw Regulators)A regulator in which the index is moved by a fine screw or cam rather than pushed by hand, allowing very small, repeatable corrections to rate.In high-grade watches of the second half of the nineteenth century
Plates & finishingMain Plate (Pillar Plate)The principal plate of a movement, on the dial side, to which bridges or the top plate, the keyless work and the dial are fixed. In full-plate watches it is called the pillar plate.With the earliest plated movements
EscapementPallet Cock (Pallet Bridge)The small cock or bridge that carries the upper pivot of the pallet arbor in a lever escapement.With the detached lever escapement in production watches of the nineteenth century
EscapementEscape CockThe cock or bridge carrying the upper pivot of the escape wheel.With bridge movements from the late eighteenth century
Keyless workBarrel BridgeThe bridge that carries the upper pivot of the mainspring barrel arbor, and usually the ratchet wheel and crown wheel of the winding work.With bridge movements from the late eighteenth century
TrainTrain BridgeThe bridge that carries the upper pivots of the going-train wheels, usually the third and fourth wheels and often the escape wheel and centre wheel.With the bridge movement (lépine calibre), which spread through French and Swiss watchmaking from the late eighteenth century
Plates & finishingMovement PillarOne of the posts that hold the two plates of a full-plate watch or clock movement apart, with the wheels pivoted between them.From the earliest plated clocks and watches
Keyless workYoke SpringThe small spring in the keyless work that presses the yoke (clutch lever) so that the clutch wheel engages the winding pinion in the normal crown position.With keyless winding and setting work in the nineteenth century
PowerReduction WheelA wheel and pinion in the automatic winding train that slow the rotor's motion down and increase its torque before it reaches the ratchet wheel.With rotor and bumper self-winding watches from the 1920s and 1930s
PowerPawl Lever (Pawl Winding)In pawl-type self-winding systems, a rocker or lever carrying pawls that pull or push a ratchet wheel round as the rotor turns an eccentric or cam.Developed in Swiss and Japanese automatics from the late 1940s; IWC's Pellaton system, designed by Albert Pellaton, is the best-known Swiss example
PowerMagic LeverSeiko's simplified pawl-winding device: a single Y-shaped steel lever whose two hooked arms pull and push a ratchet-toothed transmission wheel.1959, in the Seiko Gyro Marvel
PowerRotor Bridge (Automatic Bridge)The bridge or plate that carries the rotor's bearing and the automatic winding train (reversers and reduction wheels) on top of the movement.With rotor self-winding wristwatches from the 1930s onward
Keyless workOperating Lever (Chronograph)The chronograph lever moved by the start/stop pusher, which steps the column wheel round or moves the cam that controls the chronograph's other levers.With the column-wheel chronograph in the nineteenth century
TrainColumn Wheel and Column-Wheel ScrewThe castellated control wheel of a column-wheel chronograph, with ratchet teeth below and a ring of columns above, held on its post by a cap screw.In nineteenth-century chronographs; the column wheel remained the high-grade control method through the twentieth century
TrainCoupling Clutch (Lateral Clutch)In a lateral-clutch chronograph, the pivoted coupling lever and its transmission wheel that swing sideways to connect the running train to the chronograph centre wheel.The usual arrangement in classic Swiss chronograph calibres of the nineteenth and twentieth centuries
TrainHour Recorder WheelThe wheel that drives the chronograph's hour counter, usually indicating up to twelve hours of elapsed time.In twelve-hour chronographs of the twentieth century
Dial & handsCalendar FingerThe finger or pin on the calendar driving wheel (usually a wheel turning once in twenty-four hours) that pushes the date ring forward each night.With calendar work in watches and clocks
Keyless workDate CorrectorThe quick-set mechanism that advances the date (and sometimes the day) without turning the hands through twenty-four hours, operated from the crown or a recessed case pusher.Quick-set date mechanisms became common in calendar wristwatches from the 1960s
TrainRepeater HammerOne of the steel hammers in a repeating watch that strike the gongs (or, in older work, a bell) to sound the time.With repeating watches from the late seventeenth century
TrainStriking GovernorThe speed regulator of a repeating watch's striking train, which controls how fast the blows follow one another once the train is released.With repeating watches; anchor governors are the traditional form and centrifugal governors a later refinement
TrainWarning WheelThe wheel in a clock's striking or chiming train that carries the warning pin, used to 'arm' the train a few minutes before it strikes.With striking clocks; found in count-wheel and rack-striking movements alike
TrainFly (Fly Fan)An air brake on the last, fastest arbor of a clock's striking or chiming train: a pair of thin vanes that spin as the train runs.With striking clocks; flies are found in medieval turret clocks and in domestic striking clocks thereafterMethod
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.