Threadless headsets.
I've only seen crude drawings about the expanding star that secures the headset. As I look at it in the diagram (sorry, Lennard Zinn, but the diagrams in your book are really awful) it looks like the star fits inside the steering tube of the fork and is pulled outwards by the Allen screw when tightened, so that it makes firm contact inside the steering tube.
Is that the way it works?
I've never seen the inside of a threadless headset yet, so how mechanically strong are they?