I use SAE J844 Nylon brake line for mine, as it is much stiffer than the refrigerator stuff. I make them a bit longer than needed so they can compress a bit, cutting them at as close to a true 90 degrees as I can get. Then I chuck them up and spin them lightly sanding the burrs off and a bit of a taper to concentrate the pressure at the inside for a better seal. Works great.