I am looking to add cable guides to an existing vintage frame. I have done this in the past with brass tubing, however, brass tubing that is sold in hobby stores is thin walled, so I want something more substantial. I was thinking of steel brake line tubing, at least for the derailleur cable. Has anyone tried using some sort of locally bought tubing? If so, what did you use? I would also think that it does not actually need a tube. A piece of sheet metal can be bent into a "U" shape to act as cable guide or a piece of wire could be wound as a cable guide as well.

Or should I just spend $4 on parts and $8 on shipping and get something that I don't have to cut and shape?