On my repair..
It's actually a shouldered bolt...no threads on the last inch that locks in the notch.
It comes from the factory bass akwards, with the bolt coming from inside and screwing into the step arm from behind. Mine was gone, so I'm not sure if the threads actually run in the frame or not, almost impossible to see inside.
Got my replacement bolt all ready for when the other one disappears.
"Sticks & stones can break your bones...and hail will dent your Airstream"
So when is this..."old enough to know better" supposed to kick in?