ndard switchboards for large exchanges. In Fig. 359 are shown the
multiple and answering jacks employed in the No. 10 Western Electric
switchboard. The multiple jacks in the No. 1 switchboard are mounted on
3/8-inch centers, the jacks having three branch terminal contacts. The
multiple jacks of the No. 10 switchboard indicated in Fig. 359 are
mounted on 1/2-inch centers, each jack having five contacts as indicated
by the requirement of the circuits in Fig. 349.

In Fig. 360 are shown the answering and multiple jacks of the Kellogg
Switchboard and Supply Company's two-wire system. The extreme simplicity
of these is particularly well shown in the cut of the answering jack,
and these figures also show clearly the customary method of numbering
jacks. In very large multiple boards it has been the practice of the
Kellogg Company to space the multiple jacks on 3/10-inch centers, and in
their smaller multiple work, they employ the 1/2-inch spacing. With the
3/10-inch spacing that company has been able to build boards having a
capacity of 18,000 lines, that many jacks being placed within the reach
of each operator.

In all modern multiple switchboards the test thimble or sleeve contacts
are drawn up from sheet brass or German silver into tubular form and
inserted in properly spaced borings in strips of hard rubber forming the
faces of the jacks. These strips sometimes are reinforced by brass
strips on their under sides. The springs forming the other terminals of
the jack are mounted in milled slots in another strip of hard rubber
mounted in the rear of and parallel to the front strip and rigidly
attached thereto by a suitable metal framework. In this way desired
rigidity and high insulation between the various parts is secured.

[Illustration: Fig. 358. Answering and Multiple Jacks for No. 1 Board]

_Lamp Jacks._ The lamp jacks employed in multiple work need no further
description in view of what has been said in connection with lamp jacks
for simple common-battery boards. The lamp jack spacing is always the
same as the answering jack spacing, so that the lamps will come in the
same vertical alignment as their corresponding answering jacks when the
lamp strips and answering jack strips are mounted in alternate layers.

[Illustration: Fig. 359. Answering and Multiple Jacks for No. 10 Board]

[Illustration: Fig. 360. Answering and Multiple Jacks for Kellogg
Two-Wire Board]

_Relays._ Next in order of importance in the matter