hollow cylinder, made
up of the parts _A A' A'' A'''_, called the shell--_A_ is the great
shell, _A'_ the half shell, _A''_ the banking slot, and _A'''_ the small
shell. The brass part _D_ is called the collet and consists of three
parts--the hairspring seat _D_, the balance seat _D'_ and the shoulder
_D''_, against which the balance is riveted.

[Illustration: Fig. 171]

The first measurement for fitting a new cylinder is to determine the
height of the lower plug face, which corresponds to the line _x x_,
Fig. 171. The height of this face is such as to permit the escape wheel
to pass freely over it. In selecting a new cylinder it is well to choose
one which is as wide at the banking slot _A''_ as is consistent with
safety. The width of the banking slot is represented by the dotted lines
_x u_. The dotted line _v_ represents the length to which the lower
pivot _y_ is to be cut.

[Illustration: Fig. 172]

[Illustration: Fig. 173]

There are several little tools on the market used for making the
necessary measurements, but we will describe a very simple one which can
readily be made. To do so, take about a No. 5 sewing needle and, after
annealing, cut a screw thread on it, as shown at Fig, 172, where _E_
represents the needle and _t t_ the screw cut upon it. After the screw
is cut, the needle is again hardened and tempered to a spring temper and
a long, thin pivot turned upon it. The needle is now shaped as shown at
Fig. 173. The pivot at _s_ should be small enough to go easily through
the smallest hole jewel to be found in cylinder watches, and should be
about 1/16" long. The part at _r_ should be about 3/16" long and only
reduced in size enough to fully remove the screw threads shown at _t_.

[Illustration: Fig. 174]

[Illustration: Fig. 175]

[Illustration: Fig. 176]

[Illustration: Fig. 177]

We next provide a sleeve or guard for our gage. To do this we take a
piece of hard brass bushing wire about 1/2" long and, placing it in a
wire chuck, center and drill it nearly the entire length, leaving, say,
1/10" at one end to be carried through with a small drill. We show at
_F_, Fig. 174, a magnified longitudinal section of such a sleeve. The
piece _F_ is drilled from the end _l_ up to the line _q_ with a drill of
such a size that a female screw can be cut in it to fit the screw on the
needle, and _F_ is tapped out to fit such a screw from _l_ up to the
dotted line _p_. The sleeve _F_ is run on the screw _t_ an