PH Tool offers many different types of holes used in NDT today. Of these different hole types, the flat-bottom hole (FBH) is by far the most commonly made. The FBH is king in the ultrasonic testing world due to the simple fact that it is excellent at reflecting sound directly back at the transducer. They provide a perfect “disc-shaped,” planar reflector that can be used to set instrument sensitivity, evaluate resolution, and can be used for flaw sizing comparisons. It is also possible to create “distance amplitude” reference curves using a series of FBHs of the same size, drilled to different depths, or “area amplitude” reference curves using a series of FBHs at the same depth, but of varying diameters.