Quote Originally Posted by WeeMaan View Post
No, I ment what I said.
3/8 ID and 4/8 OD.
There is no such tube as 1/2 OD and 3/4 ID, thats impossible.

Edit: And the question has nothing to do with flow, only what looks better.
I think he meant 1/2" ID and 3/4" OD, which is one of the most popular sizes, and works great for flow rate, and looks great too. Don't be so quick to dismiss the mighty 1/2" ID tube, or as I like to call it the "Mississippi River" of tubing. Putting aesthetics over performance is sacrilege to my ears, but you can do what you want.

As for 3/8" ID and 4/8" OD tubing, I've never seen it, but that is awfully thin-walled tubing, does it even bend? It seems like it would kink even in a 45 degree semi-circle. I would think you want the walls of the tube to be as thick as possible, to prevent drooping and kinking, but maybe that's just me. Also you can forget finding compression fittings for that tubing.