* Jewels (Typically Synthetic Rubies or Sapphires): These are hard, synthetic stones (usually rubies or sapphires, although other materials can be used) that are used as bearings at points of high friction within the watch movement.
* Purpose:
* Reduce Friction: Mechanical watches have many moving parts that rub against each other. Jewels are much harder and smoother than metal, which significantly reduces friction.
* Prolong Life: By reducing friction, jewels minimize wear and tear on the movement's components, extending the lifespan of the watch.
* Improve Accuracy: Reduced friction leads to more consistent and accurate timekeeping.
* Why 25 Jewels? A 25-jewel watch is often considered the "sweet spot" for automatic and manual wind movements. It generally indicates that the movement has jewels in all the critical locations where they are needed to reduce friction, such as:
* Balance Wheel Pivots: The balance wheel oscillates back and forth, and its pivots experience a lot of stress.
* Escapement Pivots: The escapement is another critical component, and its pivots also benefit from jewel bearings.
* Gear Train Pivots: Jewels are placed at key points in the gear train to minimize friction as power is transferred from the mainspring to the escapement.
* Automatic Winding Mechanism: In automatic watches, jewels are used in the rotor and winding mechanism.
* More Isn't Always Better: While a higher jewel count can indicate a more sophisticated movement, it's not always a guarantee of superior quality. In some cases, manufacturers may add "functional" jewels that don't actually contribute significantly to performance. A well-designed movement with 17-21 jewels can often be just as good as (or even better than) a poorly designed movement with 25 jewels or more.
In summary, a 25-jewel watch typically signifies a well-made mechanical movement with jewels placed in the crucial locations to reduce friction, improve accuracy, and extend the watch's lifespan. It's a good sign of quality, but it's not the only factor to consider when evaluating a watch.