The plastic tubing that came with the gauge is 1/8. Autometer makes a copper line kit for this with 1/8 tubing which is what i am planning to get.
It will be interesting to see the readings tomorrow and whether the gauge settles. As it was mentioned in another topic, at idles it'll bounce around which it did as you can see by the numbers. For the higher rpm it wasn't "locked in" as I have read, just bouncing about +/- .5 either side of the numbers I gave. Or am I being overly pedantic about the phrase "locked in"