The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 149
Fig. 139 Fig. 140.—Scale § in; to these plugs the back board of the instrument is screwed.The plugs may be of a round or square section of about 1inch diameter or side of square. If of the latter section, theholding power is much increased by cutting the plug a littleon the twist, as shown in an…
Telephone
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