Back in the day most houses had few electrical outlets and had to use adapters to hook up other electrical items. With these adapters they could have a lamp, plug or cord extension. Today everthing is on breakers, usually one going to each set of plugs depending on the voltage needed and application. I find these old service taps facinating and just about every electric manufacturer had their own brand. This set I have represents some of the different plug styles that were mainly based on Hubbells patents. From Left To Right:C.E.M. Co. Parallel & Tandem plug, T.E.C. Co. Parallel Slots, M.E.S. Co. special loop slots, Hubbell T Slots, Bryant Polarized and Tandem slots. I couldn't imagine having to use these to hook up fans, apliances etc. but as old as they are they still work!