old porcelain "DIAMOND H" SWITCH

I bought this cheap on eBay years ago (back when eBay was still fun?!) because I thought it'd look good with the rest of my 'old switches' collection. (and for the record, I still do! <lol>) Guessing it probably controlled a fan (?) I don't really know what it first might have done, nor exactly how old it is. Its base is of white ceramic about 3" across, and its cover is metal with baked porcelain exterior. It has a very positive springloaded 'snap action' when its black pointer knob is twisted (in either direction) from position to position. Its maker's name, trademarks, and electrical specs are in small print on its side, clearly labeling it a "DIAMOND H" SWITCH. Various marks molded into its base include a patent date of March 7, 1922.