A manhole cover is lid to cover a manhole. Manhole covers are removable plates. Manhole covers provide preventive measures in that they prevent anyone or anything from falling in and also help keep keep out unauthorized material. Manhole covers usually weigh more than 50 kg, to keep them in place when traffic passes over them. Manhole covers are often made out of cast iron, sometimes with infills of concrete. Manhole covers are strong, inexpensive and heavy. A manhole cover sits on metal base, with a smaller inset rim which fits the cover.