1888

During this year, the length of the base of a light bulb was increased to accommodate more threads.  The older bases had anywhere from two or three threads.  This newer base had anywhere from four to six threads.  The base of this bulb had a copper screw shell with 4 to 6 threads (which served as one contact terminal) and one straight-sided or tapered copper contact (which served as the second terminal) at the bottom of the base, all over a plaster of paris insulator.  The base is cemented to the neck of the bulb by a thick ring of plaster of paris between the bulb and base.  There was no collar above this base as with the earlier manufactured from 1880 to 1884.  Instead the bulb had to be hand-held by its glass bowl to place and turn the base into the female threads of a socket.  Although two or three-threaded threaded bases were largely discontinued in 1888, they were still used for some applications for years afterwards.

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