Brake line tube diameter question

My stuff looks like dartfreak75 in post #6. I get the bubble for the double flare started, then with the line clamped in place, i use a small ball peen hammer to flatten it out, then i fold in the double flare with the pointed cone. I have replumbed 2 cars in the past with homemade lines using tube kits. Only had 1 leaker, had to work the seat on the flare a little more and reattach the line. That cured it.

After i bleed a system thats been opened to be repaired or assembled from a line kit, I typically will force the brake pedal down as hard as i can push it and hold it. If the pedal slowly drops as i'm holding it down under pressure w my feet then there is a leak somewhere. Time to look at every fitting in the system for fluid seepage. Most times tightening the leaking B nut a little more will correct the issue, sometimes it requires the cone seat to be worked a little more.