go inside open box and lever up from underneath enough to get under it at the top ,its that slot holds inter lock collar in place ,the ridge or shoulder on the collar fits in and holds in place (neutral) selector fork ,ie fork cant move forward or back as shoulder /ridge holds it ,spigot your removing holds the collar ,theres a slot in the collar and shoulder that pin poking out of selector shaft locates when rotated into line with fork ,fork can be moved by sector shaft but not before they are aligned ,so unless selector shaft is aligned with 5th you cant move its synchro hub by hand ,but once that spigots out you can therefore proving 5th synhro hub is ok ,click back to neutral with hub check shoulder is central of hole and refit spigot