The next thing is to get the proper heights.  This is much more easily arrived at:  the main measurement being to have the teeth of the escape wheel clear the upper face of the lower plug.  In order to talk intelligently we will make a drawing of a cylinder and agree on the proper names for the several parts to be used in this chapter.  Such drawing is shown at Fig. 171.  The names are:  The 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