Abstract: Apparatus for ultrasonically inspecting material radially bounding a circular bore into which the apparatus is insertable. The apparatus includes a central housing adapted to lie along the bore's longitudinal axis, three support arms which are engageable with the bounding wall of the bore and are circumferentially equally spaced about the central housing, linkage arms joining the support arms and the central housing for maintaining a predetermined relative configuration between the support arms and the bore wall, a transducer carrier which protrudes radially inside the support arms' engageable surfaces and is supported by each support arm, an ultrasonic transducer carried in each ultrasonic transducer carrier, means for biasing the transducers radially outward relative to their associated transducer carrier, and a pneumatically actuated cylinder which rotates the linkage arms and displaces the support arms radially outward into engagement with the bore wall.