Why are man-hole covers round?

So the covers don't fall into the holes.

And, there are other man-hole covers that are not round. I have seen pictures of square, hexagonal and octagnal man-hole covers.

What are you doing, NC? Trying to start a riot in here? Such controversy!

According to a manhole fan page, which includes photos of square ones:

"There are two reasons why manhole covers are round: 1) so they don't fall through the hole [because the diameter doesn't get smaller], and 2) so you can move them more easily by rolling them on their edges. It's not clear which of these was the primary reason round was the chosen shape." (Dan Heller's Photos of Manhole Covers)

[This message was edited by referenth on 07-12-02 at 02:28 PM.]

it is impossible for the round covers to fall into the hoe, while a square one , if turned to the diagonal of the hole will fit right through.

In addition to the above reasons there is also the question of economy. The maximum area is covered with the minimum amount of material, ergo less weight.

Plus, with any shape but circular, you've got to line up the manhole cover carefully before you place it. They're big and heavy - you don't want to spend a lot of time on micro-manoeuvring them.

They're round because the man-holes are round.

The man-holes are round because generally, the men and women who go through such holes are also round.


Mr(roundabout)Sensitive

They're also round so that when moving them, you can roll them along the ground instead of carrying them.