Abstract: In the ultrasonic inspection of test pieces, particularly tubular materials, a device for coupling a transducer to the surface of the test material, by a liquid medium, incorporates desirable features of both "contact" and "immersion" transducers. Disclosed is a coupler the housing of which has a cavity having a water supply inlet and an air exhaust vent. Water flow into the cavity if so controlled as to initially purge air from the cavity to fill it with water, after which the water flow is at a carefully controlled rate effective to keep the cavity filled while supplying fresh water only to the extent necessary to make up for water leaking out through a narrow gap defined between the test piece and the face plate of the disclosed coupler. The water within the cavity provides a liquid couplant between the test piece and a transducer carried by a holder mounted in the cavity for precision adjustment.