The black plastic spacer pieces allow you to adjust the tightness of the fit of the camlocks - don't pull them out until you have them snug or you will have a challenge getting them back - they hold the circlip out allowing the adjustable barrel to turn. When you have them all adjusted, pull the plastic tabs out and they retain that setting. Try removing one and you can see how they work - you can re inset them by leveraging the circlip.
cheers
r