Slim Blank Cover for Flush Mounted Box with 60 mm diameter/ Dünne Blindabdeckung für Unterputzdosen 60 mm

The blind cover has two parts, the base and the cover. The base gets screwed to the flush mounted box and the cover snaps onto it. 

I don't know if the 60 mm flush mounted boxes are used outside of Germany.

The snap mechanism is inspired by the great Adafruit snap fit case tutorial:

It works very well.

Cad files are attached. Feel free to remix.