1.1 ,These reference radiographs2 illustrate various categories, types, and severity levels of discontinuities occurring in steel castings that have section thicknesses of 2 to less than 4¹/₂ ,in. (50.8 to 114 mm). The reference radiograph films are an adjunct to this document and must be purchased separately from ASTM International, if needed (see 2.2). Categories and severity levels for each discontinuity type represented by these reference radiographs are described in 1.2. Note that the basis of application for these reference radiographs requires a prior purchaser/supplier agreement of radiographic examination attributes and classification criterion as described in Sections 4, 6, and 7 of this standard. Reference radiographs for other steel casting thicknesses may be found in Reference Radiograph standards E446 and E280. Reference Radiograph standards E446 and E280 provide some overlap of severity levels for similar discontinuity categories within the same energy level range (see 4.2, 5.1, and 6.3)