For brake tubes and lines, using a reformed metal tube is preferable and if factory items can't be found and emergency repair is needed, double-wall steel is acceptable. Bending brake tubes must be done with special equipment to stop twisting or kinking and an ISO flare or double inverted flare must be created with specialized flaring tools. The first step of double inverted flaring is to use a Tubing Cutter to cut the damaged part off and then gently ream the frayed area to secure a good flare. Slip a replacement tube nut on the tube, put the tube in the flaring tool and place the gauge form on the other end of the tube. Pass the tubing through the flaring tool jaws until it rests against the indentation in the gauge that fits your tube. Once positioned, tighten the tool with the bar until it is secure. Place the small end of the gauge into the long part of the tube, swing the compression disc towards the driver side over the gauge and put the tapered flaring screw into the center of the recessed area in the compression disc. Bring the tool handle to high tension, so the plug gauge is securely on the tool jaws for beginning the inverted flare. Remove the gauge and finish the inverted flare before releasing any tension. An ISO flare needs to be made with the Snap-On Flaring Tool TFM-428 or with an equivalent device. Take off the bad tube, fix any kinks inside the tube with a Tubing Cutter and put the tube nut in place. Place the tube in the flaring tool up against the top of the machine and tighten the tool bar around it. Insert and tighten the correct size adaptor onto the flaring tool yoke screw, rub a little lubricant on the adaptor, align it with the yoke screw, then turn the yoke screw until the adaptor is seated on the tool bar.