John VanSickle wrote:
> A manhole is *circular* minimize the amount of extra material needed to 
> make it impossible for the cover to fall into the manhole.

Are you guessing, or have you actually (say) worked someplace that 
designs manholes? :-)

> Minimizing the extra material is important because manhole covers are 
> heavy; 

Even six-inch wide manhole covers covering holes a foot deep are round.

> Also, a circular manhole fits in any direction.  A polygonal manhole 
> cover has to be turned to fit, or else be picked up again (these things 
> are heavy) or the corners will wear (or break) off after a bunch of 
> near-misses.

Hinges are your friend. :-)

-- 
   Darren New / San Diego, CA, USA (PST)
     "That's pretty. Where's that?"
          "It's the Age of Channelwood."
     "We should go there on vacation some time."

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