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"How would you suggest to call it in German?"

A very good question. I'm puzzled as well. It's one of those cases where a 1:1 translation doesn't really exist, as it depends on the application....

I would define it as follows:

If the protruding threaded end of a screw has been spread in order to prevent it coming loose, then that is peening.
If the metal surrouding the screw head looks as...