Budget Watch Collecting/Jewels
17 jewels is a magic number for a jeweled watch--That is the minimum number needed to jewel all the critical parts on a time-only watch. Any fewer jewels on a detached lever watch is a budgetary compromise. Note: in horology, the terms lever and pallet are interchangeable.
A pivot jewel has a hole in the center. The pivot from a staff will use that hole as a bearing.
A cap jewel (also known as an endstone) covers the end of a pivot, helps hold oil in place. When properly done, will slightly improve performance.
The impulse jewel is the main part of the balance assembly that the pallet fork contacts.
Pallet jewels are somewhat rectangular with angled surfaces, the parts of the pallet that touch the escape wheel.
The standard jewels, in order of usefulness
Balance wheel pivot jewels (2) Balance wheel cap jewels (2) (4) Balance wheel impulse jewel (1) (5) Pallet jewels (2) (7)
This would be the logical arrangement for a 7 jewel movement.
pallet pivot jewels (2) (9) Escape wheel pivot jewels (2) (11) 4th wheel pivot jewels (2) (13) third wheel pivot jewels (2) (15)
Some 15 jewel watches will include all of these jewels, while others will include the center wheel jewels but use a pin-lever mechanism in place of the jeweled lever.
Center wheel pivot jewels (2) The final necessary jewels.
Other places for jewels
Additionally, pairs of cap jewels can be added to the pivots of the fork, escape, fourth and third wheels, in order of usefulness. Cap jewels on the fork are useful but fairly difficult, while cap jewels on the train are fairly easy.
Complications can legitimately use jewels--Chronographs and auto-wind systems are two common uses of jewels
The mainspring arbor may also be jeweled. This is a marginal use of jewels.
Many watches have jewels added that do not materially improve the watch, but appeal to the "more jewels is better" belief. In some cases, a 15 jewel pinlever movement will have an extra set of cap jewels added to get to the magic 17. Timex made a very odd 21 jewel watch, based on their zero-jewel pinlever designs. In these, the balance had no cap or pivot jewels, but most of the train had cap jewels of marginal value, in addition to somewhat useful pivot jewels. Waltham made a 75 and 100 jewel watch with a standard 17 jewel movement enhanced by the addition of jewels around the rim of the watch theoretically to prevent the rotor from wearing the movement if it was impacted. see [this article on Timezone.com] for more details.