I know from my old balloon bike collecting days that there were several bikes with "expander bolt" seat posts. One that comes to mind was the Huffy Radiobike. The seatpost looked just like a stem but just straight with the bolt at the top. You had to tighten it just like you would an old stem and it used the off set angle wedge to lock it into place inside the seat tube. I also had some antique bikes that used the expander bolt seat post and another that used a system very much like a plumbing compression fitting. It looked like a headset only on the seat tube and when you tightened it a split ring, half inside the seat tube and half inside the threaded locknut, it squeezed around the seat post and locked it in place. Pretty cool, at least I think so.
Ray Homiski
Elizabeth, NJ