And here's where the fun begins. There are 4 types of tubing flares out there: 45-degree single and double flares, 37-degree single flare, and a bubble or metric flare. 37-degree is used with stainless steel lines where AN (army-navy) fittings are required (high performance). 45-degree single flares are used with lower pressure applications (carb lines, etc). The two common flares on brakes are the 45-deg double (on the left in the picture) and the bubble or Metric style (on the right in pic)