identify your lightbulb > bulb identification key


STEP 4:
Light Bulbs with Bases That Have 4 to 6 Threads [Long Threaded Bases]

Select the option most resembling your bulb from the drop-down menu to proceed to the next step. Please consult "option descriptions" for detailed info.


[The drop-down menu can be re-set by refreshing your browser window.]


FULL OPTION DESCRIPTIONS / IMAGE GLOSSARY: [Option titles are also linked to proceed to the next step.]

Note: “In 1888, the length of the screw shell or base increased from 2 to 3 threads to 4 to 6 threads.”


OPTION A: Bulb base has a copper screw shell with 4 to 6 threads and one straight sided or tapered copper contact terminal on end of base, all over plaster of paris insulator.  (NOTE: Plaster of paris is white in color, somewhat rough and porous, and easy to scratch.) [810a]


 
OPTION B: Base has copper screw shell with 4 to 6 threads and one straight sided or tapered copper contact terminal on end of base, all over plaster of paris insulator but has a wide skirt above the threads.  (NOTE: Plaster of paris is white in color, somewhat rough and porous, and easy to scratch.) [810b]


OPTION C: Entire copper screw shell (with 4 to 6 threads) and one copper contact terminal on end of base over porcelain insulator.  Plaster of paris is now discontinued.  (NOTE: Porcelain has a white, mildly translucent ceramic material at bottom of base between base eyelet and screw.  Porcelain should be a bit shinier than plaster of paris and harder to scratch.) This base was introduced in 1900. [810c]


OPTION D: Entire copper screw shell (with 4 to 6 threads) and one copper contact terminal on end of base over black or blue glass insulator.  Porcelain insulator is now discontinued.  Base is cemented to neck of bulb by waterproof cement between bulb and base.  This base was introduced in 1901. [810d]


OPTION E: Entire copper screw shell (with 4 to 6 threads) and one copper contact terminal on end of base over black or blue glass insulator but fastened to bulb mechanically without the use of waterproof cement. This base was introduced in 1933. [810e]




Pathway History:
START
2 || Tipped-Bulb-Options
3 || Base-Shape
4 || Bulbs-With-4-6-Threads

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