Standard Test Block (STB) Type A3 is used for adjusting the working sensitivity and test range, and for the measurement of refraction angle and probe index of angle beam transducers. STB types A31 (Fig. 8), A32 (Fig. 9), and A7963 (Fig. 10) are also available. • Made from 1018 Steel. • Spec: Japanese Industrial Standard JIS Z 2345 Figure 7 • Block Size: 15mm x 45.5mm x 130mm