Wristwatch Jewels

What does the “number of jewels” in a wristwatch refer to? What are they and whar purpose do they serve?

I was at a watch makers site looking at various watches. Some said “17 jewels” or “21 jewels” or more.

What does this refer to?

In a mechanical watch you have small gears or “wheels” which rotate. The axles of these wheels – “posts” – stick up through the top and bottom plates through tiny holes. A metal post sticking through a metal hole will want to start grinding away at itself. To prevent this watchmakers put tiny discs of synthetic ruby – called “jewels” – into the plates. The jewels have tiny holes in them for the ends of the rotating posts. This reduces friction and keeps the watch from eating itself alive. The higher the number of jewels the longer it should last between repairs. 21 jewels is a pretty standard number for a good quality watch.

Longines 22AS 19 Jewels movement wristwatch