Level 1: (A 15 is the smallest): green belts, sidewalks and other areas where motor vehicles are forbidden to enter.
Grade II: (minimum type is B 125): sidewalks, non-motor vehicles, car parking lots and underground parking lots.
Grade III: (minimum C250 type is selected): residential quarters, back streets and alleys, areas where only light motor vehicles or automobiles drive, and within 0.5m of kerbs on both sides of roads.
Level 4: (D400 is the lowest): urban trunk roads, expressways, expressways and other areas.
Level 5: (E600 is the lowest choice): freight stations, docks, airports and other areas. ductile iron manhole cover
Generally, it is a manhole cover with an inner diameter of 700, and a 50-ton car also needs a manhole cover based on four-axis B 125, with a weight of 60 kg.
Heavy-duty nodular cast iron double-layer Jing Zuo manhole cover bearing more than 360kN or super truck -20 main vehicle.