Hi. Can anyone tell me a little more about the old ungrounded t-slot receptacles used in the older homes?

I have heard these could be wired for 120 volts or 240 volts. The 120 utilizing the vertical slots and the 240 volts utilizing the horizintal, or tandem slots.

I would like to know what kind of appliances, tools, etc. used an ungrounded 240 volts back in the day utilizing a tandem blade plug.

Also would anyone happen to know the dates on when the T-slot was produced?

In case anyone here doesn't know what I'm talking about here's a pic:

[Linked Image from homerepairforum.com]
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Thanks.