Various
A special German standard for square covers (sewage and the like) on roads that defines the requirements for covers in the C250 ( ) D400 ( ) load class. This standard defines the size, the materials and the weight in which the lid should withstand in order to the load.

The standard title is: Gully tops 500 × 500 for road gullies, class C 250 and class D 400

Download document from Beuth Verlag (payment) https://www.beuth.de/de/norm/din-19583-1/154438471

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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The ultimate manhole covers site

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