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.
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