It is important to get the correct tube, the wall thickness has to be right for the connector to work. The nut squeezes the tube against the inner piece on the caliper or master cylinders. Look up the type of brake system you have, Matco, etc, they should have the tube type listed in the parts.
Also important to use the correct fluid for your system. Most aircraft use red hydraulic oil or ATF. Some use automotive brake fluid. The seals are not compatible with the wrong fluid.