I do not have access to a dedicated tool (can't buy one in Germany) and I'm afraid to marr it with my pliers.
You can see the knurled nut in this photograph from stringsdirect.co.uk
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I have replaced a few of these, and all I use is a pair of long nose pliers with a piece of cloth over the jaws. It is very easy to avoid scuffing the tightening ring or the surface of the scratch plate.
The tool itself is just not worth the money- it only does one thing, whereas a pair of pliers and a cloth can live in your guitar case as part of your normal toolkit.
They will ship their tools to Germany. [However, they sell many kinds of solvents, glues, stains and paints, and finishing material that they cannot ship outside of the USA due to restrictions on hazardous materials.]