Watch Jewels Explained

What a jewel actually is

A synthetic ruby, usually - lab-grown corundum, the same material family as sapphire. It is drilled with a tiny hole and pressed into the movement plate as a bearing for a pivot to spin in.

The reason is friction and wear. A gear train in a mechanical watch spins continuously for years. Steel pivots turning in brass holes wear the brass out and the movement loses accuracy and eventually seizes. Ruby is extremely hard, takes a very smooth polish, and holds lubricant well, so a steel pivot spinning in a jewel bearing wears far more slowly than one spinning in metal.

They are not real rubies in any meaningful sense - synthetic corundum has been cheap for over a century. Their value is mechanical, not material.

Where they go

Jewels are placed where friction is highest and where wear does the most damage:

• The balance staff pivots - the fastest-moving, most delicate part of the watch, oscillating several times a second, forever.
• The escape wheel and pallet fork - the components that release the gear train in controlled steps.
• The gear train pivots - each wheel between the mainspring barrel and the escapement.
• The automatic winding module - the extra jewels an automatic has over an otherwise identical hand-wound movement, because the rotor and its reduction gearing add bearings.

Why 21 and 24 are the numbers you keep seeing

A basic time-only mechanical movement needs about 17 jewels to cover every bearing that benefits from one. That is why 17 was the traditional benchmark for a "fully jeweled" watch.

Add automatic winding and you add bearings. Add a date, or a day and a date, and you add a few more. So the counts on this site land where they do:

Notice that the 4R36 has three more jewels than the 4R35 and that the difference is the day complication, not quality. Notice also that the 21-jewel Citizen 8204 sits inside a watch we rate very highly and the 21-jewel Miyota 8215 sits inside a $100 one. The count tells you about architecture. It does not rank the watches.

Why more is not better

Beyond the bearings that need them, extra jewels do nothing. There are only so many pivots in a movement, and once each one has a jewel, additional jewels are either non-functional decoration or a marketing count.

This has real history behind it. Watches advertising extraordinary jewel counts - dozens more than the mechanism could use - were common enough in the mid-twentieth century that the industry eventually pushed back on the practice. If you see a modern affordable automatic advertising an unusually high count, treat it as a claim about marketing rather than engineering.

The reverse warning is also true: a very low count on a mechanical watch - well under 17 - means bearings that should be jeweled are not, and that watch will wear faster. That is a genuine quality signal, and it is one of the checks in how to judge watch quality.

What to look at instead

If you want to compare two movements meaningfully, the numbers that actually differentiate them are:

• Published accuracy tolerance- Orient's -15 to +25 seconds a day against Seiko's -35 to +45 for the 4R36 is a real, quotable difference (accuracy explained).
• Power reserve - 40 hours against 80 changes how you live with the watch (power reserve explained).
• Hacking and hand-winding - the two features you actually use (explained here).
• Beat rate - and what it trades against reserve (beat rate explained).

Every one of those tells you something about how the watch behaves. The jewel count tells you how many bearings it has.