This International Standard specifies a bubble-point test method applicable to filter elements used in hydraulic fluid power systems. It can be used either to verify the fabrication integrity of a filter element (by checking the absence of bubbles) or to permit the localization of the largest pore of the filter element by determining the first bubble point. Verification of fabrication integrity defines the acceptability of the filter elements for further use or testing. The first bubble point is established through continuation of the fabrication integrity test. It is under no circumstances a functional characteristic of a filter element; in particular, it cannot be used for extrapolation to the concepts of filtration rating, efficiency or retention capacity and should be used for information only.