ISO 7326:2016 specifies five methods for determining the ozone resistance of the outer covers of hoses: - method 1, for bore sizes up to and including 25 mm, carried out on the hose itself; - method 2, for bore sizes greater than 25 mm, carried out on a test piece from the hose wall; - method 3, for bore sizes greater than 25 mm, carried out on a test piece from the cover; - method 4, for all bore sizes, carried out on the hose itself; - method 5, for all bore sizes, carried out on hoses that are expandable, for example textile-reinforced hoses. NOTE For hoses with built-in fittings from which it is not possible to take test pieces, the ozone resistance can be assessed on slabs in accordance with ISO 1431-1, using test sheets of the appropriate polymeric compound vulcanized to the same degree.