Reference blocks are required for ultrasonic calibration and non-destructive testing (NDT). There are already in existence sets of reference blocks constructed according to American Society for Testing and Materials standards, but as the industry evolves, we need more reference blocks with varied designs. In this study, two reference blocks of steel and aluminum are constructed. These blocks have several sets of flat bottom holes (FBH) with different diameters (0.5, 1, 1.5, 2 and 2.5 mm), angles (45° and 90°) and placements. The novel constructed reference blocks are evaluated using the ultrasonic and a displacement measuring interferometer (DMI). They allow for detailed FBH characterization in terms of defining their location, diameter, depth and so on. The two techniques show consistency in the majority of the outcomes. The expanded uncertainty of readings is found to be ±1•4 μm, according to DMI data. The findings show that the newly constructed blocks could be ideal for evaluating a variety of calibration factors including transducer sensitivity, dead zone, defect size, and depth. Furthermore, they can be used in NDT in various industries such as petroleum pipe production, steel manufacturing and so on. [ABSTRACT FROM AUTHOR]