Thickness Measurement NDTNDT techniques are used to measure material thickness in a wide variety of industries, both for manufacturing quality control and for in-service monitoring. A major advantage of NDT is the ability to precisely measure wall thickness in places where access is limited to only one side of a test piece, as in a pipe or tank, or where simple mechanical measurement is impossible or impractical for other reasons, such as part size or access limitations. Ultrasonic thickness gauges can be used on virtually any engineering material, including most metals, plastics, glass, ceramics, rubber, fiberglass, and composites.