What are jewels in a watch for?
Look through the sapphire case back of a mechanical watch and you will see small red discs set into the plates and bridges. They are not for decoration, and despite the name they are not precious stones in any meaningful sense.
Watch jewels are actually bearings, and they are a key part of why an automatic watch works the way it does, and why a well-built watch can be trusted for decades. Here is what they do, which watches actually have them, and why the number of jewels in your watch matters when you are out in the field.
The short answer
Jewels reduce friction. A mechanical watch movement is a chain of gears driven by a coiled mainspring, and every wheel in that chain turns on a thin steel pivot. If those pivots turned directly in steel plates, the metal would slowly wear away until each pivot rattled in its socket. The gear train would fall out of alignment, the watch would start losing time, and in the end it would stop altogether.
Jewel bearings prevent all of that. The pivot spins inside a polished stone that is far harder than the steel around it, so the seat stays round and friction stays low and predictable. Power from the mainspring reaches the escapement consistently, instead of fluctuating as the parts inside begin to wear. This means you get significantly more precision and durability, for a few extra pennies' worth of material.
What watch jewels are made of
Every stone in a modern movement is synthetic corundum: ruby when it is red, sapphire when it is clear. The two are chemically identical, and a trace of chromium is what makes one red. Corundum is exceptionally hard, sitting at 9 on the Mohs scale, behind only diamond, which is precisely what a bearing surface needs.
Watchmaking used natural stone from the early 1700s, but by the 1920s lab-grown material had taken over, because growing a flawless synthetic ruby is cheaper and far more consistent than finding a natural one. Jewels are not fitted everywhere in a watch. They go where the movement works hardest, the parts that spin fastest and take the most punishment.
The balance wheel never stops moving, so it gets jewels, and so do the few wheels closest to it. A wheel that turns once an hour barely wears at all, so it runs in a plain brass bearing instead. That is why most mechanical watches end up with somewhere between 17 and 26 jewels.
Jewels in hand-wound and automatic movements
A hand-wound watch is considered fully jewelled at seventeen. That covers the balance and the parts around it doing the fastest, hardest work. Add automatic winding and you have added a rotor and the gears that connect it, and those need jewels of their own, which is why most self-winding watches have between 21 and 26 jewels. Add complications on top, like a day, date and month display or a chronograph, and the number climbs again, because each one brings more moving parts with it.
Jewels in quartz watches
Quartz watches have barely any jewels. A quartz movement turns slowly and carries almost no load, so there is nothing inside spinning fast enough to need protecting. Most use one jewel, or none at all. It is why our quartz tactical watches are built around battery life, illumination and case strength instead. That is where the engineering goes when the movement is not doing the hard work.
What the jewel count actually means
The number stamped on the movement, or printed on an older dial, is a straight count of how many jewels are doing a job in there. It tells you how the watch is built. It does not tell you how good it is.
Why a higher count is not necessarily a better watch
Once a watch is fully jewelled, at 17 jewels, more jewels just mean more going on inside. What separates a serious watch from a cheap one is the case, the finishing, and how carefully the movement is regulated and tested.
Why jewels are important in a military or tactical watch
Sat at a desk, jewels give you accuracy. Out in the field they give you something more useful: a watch that carries on behaving the same way after you have given it a hard time.
Shock, vibration and corrosion
The jewels around the balance are the most vulnerable parts of any mechanical watch, so they are not held rigidly. They sit on a tiny spring that lets them move when the watch takes a hit. Drop it, fire a rifle with it on your wrist, spend hours being shaken about in a vehicle, and the spring absorbs the impact instead of the thin steel it is protecting snapping.
Corundum helps in a second way too. It does not corrode and it is not magnetic, so humidity, salt air and sweat cannot get at the bearing surface the way they would get at steel running against steel.
Holding time over a long deployment
A watch keeps good time when the balance is receiving steady power, and friction is what makes that power unsteady. A fully jewelled movement holds it steady over weeks of constant wear, where a partly jewelled one starts to drift. That is the difference between a watch that is accurate the day you buy it and one you can still trust six months into a deployment.
The jewels themselves do not wear out. What ages is the oil around them. It thickens over time until friction starts to climb, and that is what sets your service interval, not the stones.
Jewel counts across our automatic watches
All three of our automatic watches have a sapphire caseback, so none of this is something you have to take on trust. You can see the jewels working. Each one is a limited edition of 500, individually numbered.
Oconus 42mm and 44mm
The Oconus is the travel watch: military-grade build in a case that does not shout about it, made for people working across borders rather than under water. Its Miyota 9100 movement gives you day, date and month, and the extra jewels over a simpler automatic movement are there to support those three displays. It comes in two case sizes and two finishes, with five dial colors and a choice of leather, nylon or rubber straps. At 3oz it is the lightest of the three, which you notice on a long day.
Xtreme
Same 26 jewels as the Oconus, in a completely different watch. The Xtreme is the one built to go under: black DLC over solid titanium, a screw-down crown that locks, a unidirectional ratcheting bezel, and tritium tubes that glow for 25 years without ever needing light to charge them. The extra money buys the case, the 500m rating and the Swiss assembly, none of which the jewel count would ever really tell you. Two more straps, ballistic Velcro and rubber, come in the box.
US-744X
Named in tribute to elite maritime forces, the US-744X is the most jewelled watch we make. Those three extra jewels come from the way the Grand Seiko 6R20 is built and the day-and-date work it drives, not from a better-made watch, since it shares the Xtreme's 45mm case size, 5.5mm sapphire crystal, unidirectional ratcheting bezel and 500 meter rating. What the movement adds is a longer 45-hour reserve and a genuine bit of watchmaking pedigree. It is the one to pick if what is inside matters to you as much as what is around it, and built specially for saturation divers who spend days underwater, this is a watch that is mission critical, and is built to that spec.
Browse the full automatic collection, or put it up against a dive watch or a field watch from the rest of the range. Whichever way you go, the number of jewels should be the last thing you judge it on.
Frequently asked questions
17 for a hand-wound watch, and 21 to 26 for an automatic. Below 17 and parts of the movement are running unprotected. Much above 26 usually means extra displays or a chronograph, not necessarily better quality.
Only the balance and escapement are protected, and everything else is running metal on metal. 7 jewels is a budget build, common in cheap mid-century watches, and they wore out faster because of it.
A fully jewelled automatic with a few extra jewels supporting the winding system or a calendar display.
Lab-grown corundum, ruby when it is red and sapphire when it is clear. Both are grown in a furnace and machined to within a few microns.
Usually none, sometimes one or two. Nothing inside a quartz watch spins fast enough to need them.
No. Any watch driven by a mainspring has them, and an automatic is just a mainspring watch with a rotor added to wind it for you. What changes the number is how much is going on inside, not whether you wind it yourself.
