On 2004-10-19, willshak wrote:

But in any event, you can't have a pipe or tube that is 1/2"
diameter on the outside and 5/8" diameter on the inside.

I don't know about brass pipe, but in Electrical Metallic Tubing, 1/2"
EMT has a 5/8" inside diameter. The nominal or trade size may differ
quite a bit from the actual measurements.

Cheers, Wayne

P.S. I'm guessing that in the case of EMT, the outside diameter was
set to coincide with Rigid Metal Conduit, which is measured by inside
diameter, but the EMT walls are alot thinner.