Why are manhole covers round?

dave_fl

So they can't fall into the hole. May 13 00, 3:40 PM

Rhuarc

Since manhole covers are round, it is physically impossible to accidentally drop one into the manhole. If they were any other geometric shape, one could turn them askew and potentially drop the heavy thing down into the sewer. Thu May 18 12:45:46 CDT 2000 (Moved from #2632 - Duplicate question - McG) May 14 02, 9:40 AM

Son of The Household Cavalry

Even though I agree with the reasons given above, not all manholes are round. I have specified square and rectangular manhole covers on many Civil Engineering contracts. May 14 02, 10:17 AM

Sean	They're round so they cannot fall into the open manhole. If it were a square, rectangle, etc., then the cover could be made to fit into the open hole. This is not possible with a circular object. Thu Mar 08 15:52:19 CST 2001 (Moved from #10910 - Duplicate question - McG) Jul 28 02, 4:23 PM

zbeckabee

The commonly told story, which may even be true, is that manhole covers are round so some moron from Streets and Sanitation, or whatever it is they have out there in Glendale, won't be able to drop them accidentally into the manhole. A square cover you can tip up on edge and drop through the hole on the diagonal, if you follow me. Similarly with ovals. A circular hole, however, will defy the most determined efforts in this regard. This means manholes are one of the few things in the universe that are absolutely goofproof. A cover shaped like an Rouleaux triangle won't fall in either. http://www.straightdope.com/classics/a1_247a.html Feb 09 08, 4:25 PM

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