Phaeton top prop knob question

[wrndln]

I have a question about how the top prop knob stays on the top iron pivot stud. I am attaching a picture of the stud and knob. The concern I have is that the top irons need to pivot, so the knob can't be tight or it would be hard to move the top irons up and down. If the knob is not tight, it seems like it could loosen and fall off. Would some Fordbarner(s) that have a finished phaeton please explain how the knob is held in place without falling off and still allow the top irons to move easily.
Rusty Nelson