I want to get my machine optimal, and I've heard of using way oil to help keep the ways moving smooth. I see two different types of way oil at Enco, Mobil Vactra #2, and #4. They both say medium oil. This is going to be used on an Industrial Hobbies mill. Light duty use. I just don't want to keep using WD40.

#2 is most appropriate for machines under 4-5 tons or so.
http://www.mobil.com/USA-English/Lubes/PDS/GLXXENINDMOMobil_Vactra_Numbered.asp
This is the page on Mobil's website that discusses the
oil characteristics. There are a number of other Vactra's
for special purposes and other suppliers of way oil.
ISO 68 is about right for small machines.

This is going to be used on an Industrial Hobbies mill. Light duty use.

I believe if you ask Aaron Moss he would say to use chainsaw chain lube. It has a lot of tackifiers in it so will stick to vertical surfaces. Personally I use the #2 and #4 stuff you mentioned on an IH mill. The stickier of the two on the verticals and the thinner on the horizontals. I also use it on the ball-screws.

I use Vactra 2 on all my machines.

Thanks for the confirmation guys! I'm going to order a gallon of it. I hope it doesn't get used up too quickly. But I guess it's not really all that expensive.