The .75" ID and .875" OD. It happens to be the correct size for the Automag style feednecks.
I created this Zweiling using the valve tube.
Please pardon the poor pictue quality, my camera phone sucks!
The tubing works fine, and is a very good fit for the Sterling components.
As to price... It is the same as the direct feed tube. $20 per foot plus shipping.