How did they join it?

KenoLeon

Thank you for your reply.

Sorry for two different videos, I guess they have not updated some sections of their website. Previously there was a slide-in system and then they changed it to click-in.

Thank you for expanation! It is really helpful. So your suggestion is that they custom made it somewhere? I still believe that type of connector is commercially available.

So far I’ve found this one form knapp.