Del Piezo Specialties Heavy Duty Powerful 400KHz DL-43 ("hard" Lead Ziconate Titanate [PZT] Ceramic that has been modified). It features high power for high driving applications that require high mechanical stability and low energy loss. This was made for an ultrasonic medical treatment device manufacturer that went out of business. We have no data except that we know the resonance frequency is 400KHz. It is silver plated on both sides, it is 2" OD, 1.1" ID and 0.2" thick. It is brand new! Worth much more than our price!