This category is part of DIN19580 / EN 1433 Load Standard
The covers are divided into categories according to their capacity to withstand loads. These categories are marked A to F, where A specifies the lids intended to withstand the light load and F at the highest loads. The letter is usually accompanied by a maximum weight that the lod can withstand in Kilo Newton units (apx. 100 Kg). For example, the C250 represents a C-class cover that can carry a load of up to 250kN which are close to 25 tons (25,000 Kg).

D Category is used for roads and sidewalks, suitable for all types of vehicles, the D400 shows a lid capable of up to 40 tons (400 kilo Newton, or 89,920 pounds)