This Aerospace Recommended Practice (ARP) sets forth recommendations of SAE Subcommittee A-6C (Fluid Power Distribution Elements) relative to the procedure and methods to be used in the obtaining and evaluation of filter patch tests for aerospace hydraulic pumps and motors. These patches are to be used in a quality control program to insure that units are operating properly prior to delivery to the customer. This is to promote an optimum in cleanliness standards in aerospace hydraulic circuits. It is expected that this will promote a longer service life of the pump or motor.