Where does this come from, and can I check it?

Circular geometry prevents street covers from slipping diagonally into shafts. The figure is taken from Encyclopaedia Britannica, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.

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Mondo Knows Facts

Round manhole covers cannot fall through their own openings

Circular geometry prevents street covers from slipping diagonally into shafts

Circular manhole covers are widely used because a round shape cannot drop through a smaller circular hole of the same diameter, regardless of angle. Square or rectangular covers can easily slip in diagonally. Round covers are also easier to move by rolling along pavements during roadworks.

Round cast iron Manhole cover — https://www.flickr.com/photos/pasa/9039204908 · CC BY 2.0 · licence · source

Where this comes from

Encyclopaedia Britannica

Facts that can change over time are reviewed and updated. If something here looks wrong, Mondo would rather know than be confidently incorrect.

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Tags: engineering, cities, geometry

Round manhole covers cannot fall through their own openings: the short answers

Where does this come from, and can I check it?: Circular geometry prevents street covers from slipping diagonally into shafts. The figure is taken from Encyclopaedia Britannica, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.
Is this really a everyday life fact?: Yes. It sits on the Everyday Life shelf, one of 1,090 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.
What else can I read about it?: The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.