Tube flaring is designed to provide an air-tight or fluid-tight seal at the end of a tube, usually applied in hydraulic connecting fittings, it improves accessibility to the interior of the tubing.
The flared joint is close to the fitting and tightly fixed in place with the nut, no gasket or seal is required to prevent leakage.
The end is usually flared to a 37° or 45° angle. 45-degree flares are the most common in automotive direction(brake lines). AN or Army-Navy fittings require 37-degree single flares.
There are three types of flares. Single flare and double flare and bubble flare.
Single flares are easy to crack and leak, only suitable for low-pressure connection demand.
Double flares(also known as SAE and Inverted Style Flare) will fold the material twice, it is more durable and sturdier, it can bear high pressure and make the connecting tighter, can prevent the pipeline connection from crack and leak, usually used in high load connection requirements such as vehicles.