Inverted flare is a 45 degree double flare that is used to connect hard line to a component. It is commonly utilized in a vehicle's fuel, oil and brake systems. The tube nut pushes the flare against the seat at the bottom of the components port, forming a leak-free seal. Every day wear and tear can result in cracks or deformations that may require you to cut and reflare the hard line, or replace it entirely. Inverted flare does not seal utilizing the threads but instead forms a seal with the 45 degree flare at the end of the tube, so if you have a double flare that is leaking, teflon tape will not resolve the issue. The fluid is leaking past the flare and will find a path between the tube and the nut. When mating a new flare to an old component, you may need to loosen and re-tighten the tube nut several times before it forms to the seat and creates a proper seal. Use of a line wrench will ensure that you get good torque without stripping the tube nut.