There is also http://www.espimetals.com/index.php/online-catalog/824-Aluminum which is a vendor our Caltech cryo expert Matt Hollister likes to use. 6N sounds expensive. If weight isnt an issue, I have a hard time thinking that 6N Al is the correct solution. And you will need to make the end pieces out of Al 1100 in order to have similar metals and welding, or do the cranking down solution that Chris came up with. I would think that 5N or OHFC copper with OFHC copper ends would lack the 1100 bottle neck and be cheaper and better...But I guess others have thought of this a lot, just my sort of informed 2cents. Zak