Every part of a watch movement, from screw to pinion

Borna Bošnjak

Even in our niche little world of dedicated watch enthusiasts who tend to fawn over the latest and greatest, we can only briefly touch on all the parts that come together to make these little ticking devices, well… tick. Most people reading this will know the usual watch part terminology – case, bezel, hands, and the sort – but if you’ve ever wished to delve deeper into what hides behind those dials, this is a good place to start. Now, I will quickly admit that this article will perhaps make seasoned watchmakers scoff as I’m only going to skim the very surface of watch movement components and their roles. With that acknowledgement out of the way, it’s also worth saying that these are only the most common ways of putting together a watch movement, and will not include mentions of exotic complications and escapements, nor decoration methods – rather think about it as a breakdown of your bog-standard ETA 2824. So, if you’re a watch nerd who is tired of having to explain how that spinning thingy on the back of a watch can power it, we’ve created this handy guide that you can now send them, and save yourself countless hours.

Jewels and screws

blued screws line up — Heat-blued and purpled screws. Image courtesy of Jose Manuel Mora

Let’s start with the parts that actually keep the whole show together and running. Screws are screws, and are used to… screw things down? This is going well, isn’t it? Jokes aside, these numerous tiny parts can be some of the most difficult to produce and are often outsourced to large-scale productions, though the finest artisans still make them by hand.

Top – regular jewel bearing. Bottom – bearing with a cap jewel.

The jewel count is something you may see listed on a spec sheet, and it relates to the number of corundum crystals (usually synthetic ruby or sapphire) in your movement. They’re most often used for doughnut-shaped (or torus, if you want to be fancy) bearings, with the central hole housing the spindle of a gear thanks to their low friction, usually necessitating only a small amount of lubricant to be used. You may find some bearings to have two jewels, with an additional cap jewel stopping the spindle from unwanted movement.

Jewels are also used in the escapement, most notably for the two prism-shaped jewels of the pallet fork, and the impulse jewel of the balance wheel – more on which shortly.

A. Lange & Söhne Datograph Up:Down Blue movement 1 — The many intricate finishes of the Datograph Up/Down movement punctuated by the red synthetic rubies and blued screws.

Though it’s not a hard and fast rule, generally, the more jewels a movement has, the more complicated it is, as it could mean that there are more moving parts, and hence more features. Most basic, manually wound watch movements will feature around 17 jewels, while automatic ones tend to sport between 21 and 25 jewels.

The support structures

And where do those jewels and screws sit? Those would be the plates, bridges, and cocks that hold the numerous other components. Most modern movements have a combination of these three types, though certain manufacturers, notably those from Glashütte, have continued the use of large plates that were much more commonplace earlier on. The Lange Zeitwerk Lumen above is notable for its large three-quarter plate, with three cocks off to the left side for the balance and some wheels of the gear train.

vacheron constantin traditionnelle manual winding movement caseback — Vacheron Constantin’s calibre 1440

In the example of the Vacheron Constantin Traditionnelle above, you can make out three distinct supports that are more similar to a basic manually wound arrangement. These are the barrel bridge, train bridge, and balance bridge. Just a note on differentiating between a plate, bridge, and cock. Plates are large structural pieces with multiple screw points to the main/baseplate (more on which shortly). A bridge usually only has two screws securing it to the baseplate, though you can at times see the word bridge and plate used interchangeably. The most notable difference here is the cock, which only screws into the baseplate with one screw, and cantilevers the rest of the way. Let’s break these down further, and mention some additional components.

Once again referring to the Vacheron movement above, and starting with the barrel bridge, we can see it containing the crown wheel (to the right of the crown) which is meshed to a larger ratchet wheel that sits on top of the barrel. To the right of the ratchet wheel is the click – I’ll explain the barrel assembly in more depth shortly.

tissot heritage petite seconde movement caseback — The manually wound movement of the Tissot Heritage Petite Seconde

Next up is the train bridge that holds the gear train. In the Vacheron movement, we see the large centre wheel being being held by the train bridge, though some movements (like the Unitas in the Tissot above) choose to hold the centre wheel in the barrel bridge (making it more akin to a plate).

This hand-wound movement also does a great job of showing off the assembly of the pallet and balance, which is actually composed of a bridge and a cock in this case. The polished section sitting just beneath the balance wheel, held in by two blue screws, is the pallet bridge, and holds the pallet fork. Above sits the balance, cantilevered by the balance cock. Comparing against the Vacheron movement, you’ll see a balance bridge used instead, secured to the baseplate with two screws.

rolex 3230 — The Rolex 3230 found in the likes of the Rolex Explorer ref. 124270

Just very briefly touching on automatic movements and the automatic bridge or block. This is the part connecting the rotor to the automatic train, and then onto the barrel assembly, though it’s not always necessarily used. Sometimes, brands will prefer to just use a large plate to cover the top part of the movement instead.

mcgonigle tuscar mainplate — The mainplate of the McGonigle Tuscar. Image courtesy of The Naked Watchmaker

And finally, the bit that everything connects to. Think of the mainplate as the guideline to putting together the very complicated pieces that make up the rest of the movement, with correctly positioned screw holes, levels, etc. Just to get you oriented properly, the back of the mainplate has a protruding pinion that the hands will connect to, with the back of the dial being pressed against it.

Keyless works and crown assembly

h moser cie cylindrical tourbillon wrist close up — The H. Moser & Cie Cylindrical Tourbillon’s keyless works

Now that you know the base structural elements, let’s get into how the watch actually works. The most common point of interaction will be the crown, so let’s start there. You’ll most commonly use the crown to wind and set the watch, while also potentially being able to interact with some of the watch’s complications, if there are any. But why do we call them keyless works? That’s due to early pocket watches needing a key to do the job of a crown. The basic form of the modern keyless works was invented by Adrien Philippe, later of Patek Philippe, in 1844, although other versions were introduced up to 20 years earlier, it was Philippe’s concept that proved the most useful and has stuck around until today.

Attached to the base of the crown is the winding stem, and as the crown is pushed in or out, a groove on the winding stem will interact with the setting lever that locks the crown in the desired position.

Coaxial (in other words two things mounted to the same axle) with the winding stem is the castle wheel, which is in the shape of a barrel, bisected by the yoke, with teeth on each end. Also called the clutch or the sliding pinion, it engages the winding pinion with teeth close to the crown to wind the watch when the crown is pushed in. When the crown is pulled out, the inner teeth engage the intermediate wheel meshed to the motion works to turn the hands.

Barrel

vacheron constantin ref 4302 openworked movement caseback — The skeletonisation of the Vacheron Constantin ref. 4302 allows a look inside the barrel

The barrel is the main energy store of your watch, topped up either by its automatic winding rotor or input from the crown. For now, we’ll focus on the manually wound portion. As the crown is turned, it engages the winding pinion that’s meshed with the crown wheel. You can see the crown wheel above, with its three screws and wide spokes that look like a radiation warning icon.

The crown wheel meshes with the larger ratchet wheel that sits on top of the barrel itself. Here, the ratchet wheel is skeletonised, with three screws near the centre of its axis. To the right, you can see the oddly shaped and polished click, which ensures winding can only be done in one direction, not allowing the barrel to move in the other.

Through the spokes of the ratchet wheel you can see the actual inside of the barrel – this is usually not displayed like this due to this movement’s extensive skeletonisation. The mainspring that sits inside the barrel is connected to the arbor of the ratchet wheel, coiling up as the watch is wound, acting as a store of potential energy, and slowly uncoiling and providing power to the gear train.

Gear train

patek philippe 215 ps — The delightful Patek Philippe 215 PS. Image courtesy of Watch Club

Okay, now we’ve got power – but where does it go? Down the gear/wheel/going train, of course! Starting with the first (or great) wheel which is the barrel itself, its arbor (shaft) meshes with the gears of the second (or centre) wheel. The second wheel turns once per hour, and drives the cannon pinion as well as the pinion of the third wheel. In the Calatrava movement above, the second wheel is placed centrally, but in movements that sport a centre seconds hand, the second wheel is placed to the side, allowing the fourth wheel that drives the seconds to be placed centrally.

The third wheel acts as an intermediary between the second and fourth (to the left and up of the second wheel in the image above), driving the pinion of the latter. As mentioned before, the fourth wheel is used to drive the seconds in most watches, but also meshes with the escape wheel. Notably, in movements with a slow beat rate, the fourth wheel can be omitted completely, and the escape wheel is then driven off the third wheel.

Sitting at the end of the gear train is the escape wheel, its shaft held by the large, gold-rimmed jewel in the upper left of the balance wheel. The escape wheel is continuously locked and unlocked by the pallet fork, allowing the escapement to function and providing impulses of energy to the rest of the gear train – but more on the escapement shortly.

Motion work

Before we get there, we have to talk about the motion work. It’s essentially a reduction gear that drives the hours based on the minutes, powered by the centre wheel. Starting with the cannon pinion that’s hollow and coaxially fitted to the second wheel shaft, it holds the minute hand. Teeth on its arbor drive the minute wheel set off to the side, which at its pinion meshes with the hour wheel with its hollow shaft fitting over the cannon pinion and centre wheel shaft. The entire assembly results in the hour wheel rotating once for every 12 full rotations of the cannon pinion.

During setting, the minute wheel is instead driven by the intermediate wheel from the keyless works, and adjusts the cannon pinion and hour wheel, hence moving the hands. But, how does this not affect the rest of the going train? As the cannon pinion is friction-fit over the second wheel shaft, this friction is set just right to turn when affected by the going train. However, when the hands are being set, the force overcomes the friction and allows the motion work to turn independently of the going train.

Escapement

And now for the most delicate and most important part in any watch movement – the escapement. It’s the mechanism that’s responsible for the accuracy of your watch, and takes numerous forms, and is essentially a way of regulating the release of mechanical energy in measurable, accurate bursts. For the sake of simplicity, we’ll focus on the most common escapement that’s used these days – the Swiss lever.

To explain the Swiss lever, let’s start with the end of the wheel train, and the escape wheel. The escape wheel is under tension due to the torque that is applied to it by the mainspring on the other end of the wheel train, but the wheel train cannot advance while the escape wheel is locked.

The motion of the escape wheel is controlled by the pallet fork and its two jewels – the entrance and exit pallets. The other side forms the actual fork shape, with the shaped middle part made as such to interact with the impulse pin of the balance wheel, usually another jewel. The motion of the pallet fork is restricted by the two yellow banking pins, and its movement powered by the back and forth oscillations of the balance wheel.

At rest, it takes a tiny amount of force applied to the lever fork by the balance wheel and impulse pin to unlock the entrance pallet and allow the escape wheel to rotate clockwise by a small amount, before being locked by the exit pallet. As the balance wheel is now swinging, it will get pulled back by the balance spring (not shown in the animation above), and swing back the other way, reversing and repeating the process with each swing of the balance.

The balance wheel itself is comprised of the roller that houses the impulse pin, the balance staff that serves as the axis of rotation, and of course, the hairspring. Most modern movements will also house some sort of shock-resistance technology that is fitted to either end of the balance staff, where the jewels are mounted with springs rather than rigidly. The best-known example of this is Incabloc, invented in the 1930s.

hublot big bang ceramic integrated etachron — Hublot’s Sellita base uses an Etachron regulator.

An escapement is also most often fitted with a regulator, which allows the wearer (or more commonly, their watchmaker) to make small adjustments to the timing of the watch. As you would’ve learned by now, there’s more than one way to do anything when it comes to watch movements, and the same goes for regulators. The ones you commonly find are swan neck or Etachron regulators, the latter being really popular and adopted way beyond its inventor, ETA.

fleming series 1 movement caseback free sprung balance — The free-sprung balance of the Fleming Series 1.

Usually reserved for higher-end watches, balances can also be free-sprung. These usually come pre-adjusted from the watchmakers, with further adjustments done by way of small weights placed around the rim or on the spokes of the balance wheel.

Automatic train

And just to complicate things a tad before finishing up, I can’t omit mentioning automatic winding, but it once again comes with a disclaimer of not involving peripheral, nor micro-rotors. Characterised with a large, centrally mounted, oscillating weight, automatic movements negate the need for hand-winding, with some completely removing the feature altogether (famously Seiko’s 7s26). The winding rotor is attached to the automatic train via the central ball race, where it interacts with the winding wheel.

This is essentially another ratchet and click mechanism that allows the spinning oscillating weight to wind the barrel. Simpler movements only allow the rotor to wind the movement in one direction. If you do want your movement to wind in both direction, you’ll have to incorporate some sort of reversing wheel assembly. A common solution is two meshed wheels, only one of which has a pinion that drives the rest of the automatic train and winds the barrel. Other, more complex solutions do exist, such as coaxial reverses housing two separate clicks around a central ratchet wheel.