On Sun, 08 Jun 2008 08:32:33 -0700, Darren New wrote:

>> 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. :-)

Hinges introduce additional complexity and are subject to breakage under 
stress...

Jim

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