Miller, Kempster Blanchard, 1870-1933 · New York : McGraw publishing company · leaf 534
. This jack represents the highest development in theconstruction of a three-contact jack for multiple switch-boardwork. There are no make-and-break contacts between the jacksprings, all contacts being normally insulated from each other andadapted to engage only with the plug contacts during use.…
Telephone
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