Double flare right? Okay, for anyone interested here are the steps:
1. Of course, cut the tube, and make it straight. Get rid of any burrs on the inside (I use a small circular file).
2. Put the tube you're working with in the correct sized hole on the flaring bar. Take the appropriate sized adapter and place it flat side down on the bar next to the end of the tube. The end of the tube should usually stick out to the first "step" in the adapter. Next, tighten the side nearest the tube first, then make sure the other end is really tight. The little teeth in the hole are what grip the tube and prevent it from slipping. Here are the tube end and adapter side by side, and me tightening the clamps on the bar with a screwdriver for leverage.
3. Place the stem of the adapter in the tube, and put the yoke assembly in the center of the adapter. Tighten that baby down until it squishes the end of the tube against the bar.
4. Remove the yoke and adapter. Put the yoke back on without the adapter, and tighten all the way down again making the tube end form a bell shape, a 45 degree flare. Don't go too crazy with the tightening or you might split your new flare.
Loosen up the yoke again. Ta-da! you've made an honest to goodness double flare. Now you can make all of your friends jealous.
I think the real trick is getting the wingnuts on the bar nice and tight. If not then the tube will slip. Old worn out flaring bars do the same thing.