The wall should have at least 20 cm, otherwise the spring cannot build up the force to hold it together.

We have already sold the door clamp, so unfortunately I can't check it.
But the thickness of our door is 22 cm.
If I remember correctly, it was always quite difficult to mount because of the door thickness.
So I would estimate it to be 23-24 cm at the most.

dslé I could tell you because I don't have the strength to spread it to its maximum but about 5 to 7 cm more than the door wall