The entire copper threaded base has 4 to 6 threads over a black or blue glass insulator and one straight-sided or tapered copper contact terminal at the bottom of the base. The base is cemented to neck of bulb by waterproof cement between bulb and base.  Bases with glass insulators were introduced in 1901 and have been in use ever since.  However, the use of waterproof cement was discontinued in 1933 with the advent of mechanically attached bases. [See A82]



 
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