You said it best, .320 is the new 3/8" ID, or I am just wrong about auto tubing! Think about it how small is 5/16" then.

I measure conduit all the time and it's always under a little, but never over the size I was using. even when I put it in a bender it looks smaller compaired to the shoe that bends it alot of tubing and conduit is made in CHINA now, not the USA.