I just discovered this beast in an old piece, and figured very few others have encountered it either.
How to describe? I can't find a drawing in anyone's catalog.
The two outside throw positions connect to the center pins as normal in an on-on type. The center position has each center pin connected to one throw position, but opposing position from the other. Like separating the toggle into two distinct switches in opposite position from one another.
It's used to make a three position toggle switch have fast/medium/slow or low/medium/high settings, as opposed to fast/slow/medium or low/high/medium settings you get trying to use the more common on-off-on type.