How do you mount the rear license plate on a Euro?

Hi all,

Newbie here to this forum, though I have owned my 78 Euro 5 speed for 29 years; brought it back from Germany as a gray market. Yesterday as I left the office to go home I found that someone who apparently needed it more than me had stolen my rear license plate. In trying to mount the new one, I can't recall how it bolts on (darn CRS). I thought the two screws had plastic nuts behind the rubber spacers, but nothing like that is left now. The screw holes aren't threaded like the front ones are, so how is the license plate attached? I didn't have a bracket; I just drilled holes in the US plate to match the mounting holes.

Thanks,
Greg