SAE J514 is the standard for 37 degree flare fittings. The 37 degree angle is preferred for harder materials such as steel as they are prone to cracking when flared out to 45 degrees. The angles of the male and female ends should be the same. However, though it might not be good practice, you can install a 45 degree female flare on a 37 degree male fitting and it will seal. The reverse is not true.