http://www.astrodigital.org/space/stshorse.html
At least they're actually the dimension they're claimed to be, and you don't have to ponder questions like "Why won't a three-"inch" pipe fit into a four-"inch" stud space?"
I have pondered the last question for years... I mean, three inches is less than four inches but...
Why not 120mm^2...............Where did they come up 4 11/16" why not 4 3/4" or 4 1/2" ect.