Originally Posted by jimmuller

dbakl's explanation is quite accurate, no further explanation necessary. Your original description was that "a bolt went through to a bolt on the back of the dropout", or something similar. What you meant was a bolt from the upper knuckle of the derailleur went through the dropout hole to a special nut that fits on the inside of the dropout.

As I recall, that's how all the Simplex Prestige units worked, though they typically attached to a claw instead of a dropout hanger. The flange of that special nut was thin enough that it didn't interfere with the small cog, and it had a flat side that went to the front to allow more room for the axle to come back. The only way it would have worked with a dropout with integrated hanger is for the nut itself to fit into the threads, or else it didn't protrude into the threads at all. In any case, if your dropout has good "Campy" threads you can just screw the Suntour into it.