Loc: Wharton, Texas, USA
I saw one of these plates some time back in the front hall of a turn of the century house here. The handles for two tumbler switches extended through the holes - as celtic said, a couple of switches on a single yoke. I did not get to actually see the switches themselves, but imagined they were probably not too much different from the combination devices available today (switch/switch, or switch/receptacle).
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