I did a few searches about what the inner diameter measurement should be for 3mm carbon tubes, but didn't really find a solid answer. I was going to order the 3mm x 1.5mm x 1000mm tubes from rcfoam, but there are a few other options. So I thought I'd see what others are using.
Try my new "RC Sidekick" Android app, available at Google Play
The 3mm OD tubing with a 2mm ID works fine and is slightly cheaper per tube.