Tonpilz transducers have a center bolt to prevent the ceramic being subjected to a tensile stress during part of the alternating stress cycle. Two points in the transducer design are analyzed; one is the calculation of the peak stress (the method presented used the voltage applied to the ceramic during the transmitter pulse, and measured values of the electrical admittance of the transducer), the other is the control of the pre-stress imposed by the center bolt. The pre-stress should be larger than the calculated peak alternating stress, and it can be controlled by measuring the voltage or the charge generated when the bolt is tightened.