Pull-pin assembly with wear button (small white plastic insert in the tip). The threaded end of this pin is what the pull knob screws onto, which when pulled unlocks the rack to be turned. The tapered end locks into the upper mounting plate's position holes to lock into place.
Wear button can also be purchased separately as can the pull-pin. Since the wear button protects the bottom of the upper fork mount from damage, if it is worn or missing the pull-pin can scratch/gouge the mount.