Abstract: A rotary ultrasonic testing apparatus includes an annular stator; an annular rotor mounted on the stator for rotation about a workpiece to be tested as it is moved through the stator and rotor; and an ultrasonic probe assembly mounted for rotation with the rotor, said probe assembly comprising a cranked arm pivotally mounted at the crank thereof upon a bearing pin having an axis parallel to the axis of the rotor, the cranked arm carrying towards one end an adjustable counterweight and at the other end an ultrasonic probe block and guide shoe for facing to the surface of the workpiece, said bearing pin being adjustable in position relative to the rotor axis, spring means for limiting movement of the arm about the bearing pin, and water supply means connected to the probe pad.