How does this radio ground?

[6670charger]

How does this radio ground?

I will be buying a 92 525i Wagon in a few days. This is a European spec car and located in Germany. The car has no radio in it right now, but, I found and purchased a factory radio and its wiring harness plugs from a junked similar vintage 7 series car. I assume most of these radios interchanged in some fashion, and that all I have to do to hook it up is splice the matching wire colors in the dash to the wires to the plugs for the radio.

My question is, how does this radio ground? Does the threaded stud in the middle of the radio (rear view) ground to the body? There doesn't seem to be a specific ground wire, unless the Germans use a color other than black to designate ground.

I've attached a few pics of the radio front and back to help show what I mean.

Any suggestions would be helpful.

Thanks.