@swurl then the most simple is to read the code of QDial and create your own based on it.

@J-Hilk Thanks ...I tried this.

@raven-worx
Sorry if I wasn't specific enough. I solved the problem now; all I had to do was instantiating the filter and setting up the signal-slot-connections in the mainwindow.cpp and additionally (that's what I didn't grasp at first) calling

app.installEventFilter(win->filter);

in the main.cpp (win being the mainwindow object).

Thanks a lot for your help!