I have a hard time dismantling the group shower of a La Scala Butterfly. The main problem is, that there is —as I have seen so far on other machines— any visible screw nut on the bottom of the sieve. It is stuck, does not turn, even by force using a pipe wrench.
After thinking about this for days, reading every repair or rebuild history I could find in the internet, I realized that there is one more possibility. The sieve is mounted bottom facing and as it is an exposed part, facing a lot of shaking on the most outer edge (and as the La Scala engineers have shown some engineering details that already impressed me), it could be that the thread is milled counter clockwise.
And yes, it is. Edit, which I forgot: It just stuck due to the massive amount of old coffee. There was no thread at all.