A self-aligning probe assembly has one or more ultrasonic transducers adapted to transmit an ultrasonic shear wave into the inside surface of the hollow structure such as an aircraft fuse pin and to receive the shear wave emerging from the inside surface of the hollow structure. The nature of the received shear wave indicates the presence of flaws or damage in the inspected part. The probe assembly can be used to inspect fuse pins on aircraft without having to remove the aircraft engines.