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Manhole Covers


Traditionally made of cast iron, steel or concrete, manhole covers can also be made of fiberglass-reinforced plastic, which offers corrosion resistance. Why are manhole covers round?


A round manhole cover is larger in diameter than the ring on which it sits, as well as it holds its shape through freeze-thaw cycles better than square openings which may skew becoming trapezoidal.
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Comments

  1. Unknown4/13/15, 9:11 PM

    So they don't fall through the hole. Square/rectangular may fall through diagonally.

    ReplyDelete

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