Tuesday's Puzzler

Tuesday's puzzler:
Why did the inventor of man-hole covers choose round ones, since square ones were easier to make?
Answers only accepted to mark.mcguire@btinternet.com
Points have been are awarded as follows:
Byte = 5
Richard = 4
ADMS = 3
Gina from Canada = 2 points
Clair from Sendit.com - 1 point