Cracked aluminum block compares sensitivity of different penetrants or sensitivity of old and new penetrants. Complies with ASTM, MIL and ASME codes. Pressure code, section V & III, MIL-I-25135 and AMS-2644. The cracked aluminum block is made from SB-211 Type 2024 aluminum, rolled 3/8 inch thick with dimensions of 2 x 3 inches. A notch separates the block's two sides to facilitate side-by-side comparisons.