Convertible Lamp Bases

The picture shows two lamps that could be used in one of three sockets — the Edison, Thomson-Houston or Westinghouse. The lamp on the left could be used in a Thomson-Houston socket, as shown; the base threads that are visible would not have been used. A tapped hole is in the bottom of the base for contact with the T-H socket. If the threaded piece shown is screwed into the center tapped hole the base would be converted into an Edison base and the threads would therefore become functional.

In the picture to the right the same type of lamp base is shown but the small screw contact would convert the base so that it could be used in a Westinghouse socket. Thus, with either lamp, if the small screw contacts were available, the lamp could be used in three different sockets.