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This document specifies a grid rating system that provides a means of defining levels of performance of anodic oxidation coatings on aluminium and its alloys that have been subjected to corrosion tests. This rating system is applicable to pitting corrosion resulting from — accelerated tests, — exposure to corrosive environments, and — practical service tests. This document takes into account only pitting corrosion of the basis metal resulting from penetration of the protective anodic oxidation coating. NOTE 1 ISO 8993[1] describes a similar rating system based on defined chart scales. NOTE 2 The grid rating system is frequently used for rating the results of short-term corrosion tests for relatively thin anodic oxidation coating, such as those used in the automotive industry.