... Iron 1) Product information: Manhole covers are manufactured for road construction, natural gas, water supply and drainage, telecommunications. Manhole covers and gratings ... should be smooth, no blisters, holes, distortion or any other defects. 2) Material A) Ductile Iron ... 400-12, GGG600-3, GGG700-2 B) Grey Iron GG20, 25, 30, 35 3) Designs A ... or as per customers' requirements. cast iron grating