Jewels are of four distinct
types, each type having a particular function.
HOLE JEWELS.
Hole jewels are used to form the bearing
surface for wheel arbors and balance staff pivots.
CAP JEWELS.
Cap jewels are flat jewels. They are posi-
tioned at the ends of wheel staffs, outside the hole jewels, and limit
the end thrust of the staff.
ROLLER JEWELS. The roller jewel (pin) is positioned on the
roller table to receive the impulse for the balance from the fork.
PALLET JEWELS. The pallet jewels (stones) are the angular-
shaped jewels positioned in the pallet to engage the teeth of the
escape wheel.
e.
Number and Location of Jewels.
Ordnance watches have
either 7, 9, 15, 17, or 21 jewels. The location of the jewels varies
somewhat in different makes and grades, but the general practice is
as follows.
7-JEWEL WATCHES.
Seven-jewel watches have: one hole
jewel at each end of the balance staff; one cap jewel at each end of
the balance staff; one roller jewel; and two pallet jewels.
9-JEWEL WATCHES. These have the seven jewels mentioned
in 7-jewel watches, with the addition of a hole jewel at each end of
the escape wheel.
15-JEWEL WATCHES. These watches have the nine jewels
found in 9-jewel watches, with the addition of the following: one hole
jewel at each end of the pallet staff; one hole jewel at each end of the
fourth-wheel staff; and one hole jewel at each end of the third-wheel
staff.
17-JEwEL WATCHES. The 15 jewels in 15-jewel watches are
used with the addition of one hole jewel located at each end of the
center wheel staff.
21-JEWEL WATCHES. These have the 17 jewels found in 17-
jewel watches, with the addition of: one cap jewel at each end of the
pallet arbor; and one cap jewel at each end of the escape wheel staff.
