1.1 These digital reference images illustrate various categories, types, and severity levels of discontinuities occurring in steel castings that have section thicknesses of 2 in. (50.8 mm) to less than 4¹/₂ in. (114 mm). The digital reference images are an adjunct to this standard and must be purchased separately from ASTM International, if needed (see 2.3). Categories and severity levels for each discontinuity type represented by these digital reference images are described in 1.2.