Thanks for the reply, Glend. It looks like this:
http://www.teleskop-express.de/shop/...itage-130.html
And the nut wobbles. The threaded part of the holder is a bit worn out, so no wonder... Bunnings said it is a cheap metal because threaded parts should last much longer. They said it should certainly be covered by the warranty, so I am going to contact them... But I don't know how long it will take. Any experience with SW warranties?
It has ALWAYS been loose, so maybe I should have contacted them at the very beginning, but now it got much worse.