ISO 19631:2015 specifies performance and quality requirements for the qualification and manufacture of standard tube fittings to ensure reliable performance in aircraft hydraulic 5 080 psi (35 000 kPa) systems. ISO 19631:2015 specifies baseline criteria for the design and manufacture of system fittings that are qualification tested on engines. ISO 19631:2015 covers fittings from size ?04 to ?20 used for the following: ? separable/permanent pipe end fittings; ? permanent connection fittings; ? separable connection fittings. ISO 19631:2015 covers fittings of the temperature types and pressure classes specified in ISO 6771.