Reference Radiographs are nondestructive testing standards universally accepted because of their high reliability in accept-reject actions. These reference radiographs illustrate various types and degrees of discontinuities occurring in thin-wall steel investment castings. (The reference radiographs are considered to be applicable to all thin-wall steel castings, requiring close tolerances. Such castings generally include those made by the lost wax, frozen mercury, ceramicast or shell mold processes.) They are intended to provide: A guide enabling recognition of thin-wall steel casting discontinuities and their differentiation both as to type and degree through radiographic examination. Example radiographic illustrations of discontinuities and a nomenclature for reference in acceptance standards, specifications, and drawings. The set of reference radiographs, produced with X Rays in the range from 130 to 250 kVp, consist of 16 plates 8-1/2 by 11 in. (216 by 279 mm) in a 9-3/4 by 11-1/2 in. (248 by 292-mm) ring binder.