Various
The ultimate manhole covers site
A German standard of the German Institute for Standardization ( ) for manhole with frame for vehicular and pedestrian areas
From the standard overview:
Gully tops and manhole tops for vehicular and pedestrian areas - Securing of the cover or grating within the frame

Download document from Beuth Verlag (payment) https://www.beuth.de/en/standard/din-1229/238124687

An example of a cover that carries the standard on the "ultimate manhole covers" site. From this lid the picture that appears in the general section was taken.
There are 19 manhole covers in the site that has this standard
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The ultimate manhole covers site

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