Various
A German standard 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.
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