A system and method for ultrasonic examination of a threaded test object, and more particularly, the mounting threads of a compressed gas tube while the tube is affixed to a tube trailer is provided. The disclosed ultrasonic test instrument includes a probe having one or more transducers for transmission and reception of ultrasound pulses, a contoured wear plate, and a shoe of highly attentuative material having a thread-like exterior surface adapted to mate with the threaded surface of the test object. The shoe further includes a narrow window in the thread-like exterior surface such that the shoe absorbs most of the ultrasonic pulses transmitted from the piezoelectric crystal except for the ultrasonic transmissions passing through the narrow window to the test object.