Abstract: An ultrasonic piezoelectric transducer and a method for measuring and/or monitoring the thickness of a wear member, in-situ, and the amount of wear that has occurred thereto, is disclosed. The transducer includes a sleeve which is received in a blind bore provided in the wear member, a piezoelectric element positioned within the blind bore, and an aligning spacer means interposed between the end of the sleeve and the piezoelectric element. By the application of appropriate voltage pulses to the piezoelectric element, the wall thickness between the bottom of the blind bore and the inner surface of the wear member can be measured.