Vktech 12Pcs 27mm Piezo Discs with Leads Mic Drum Trigger Acoustic Pickup CBG Guitar Plate material: Brass Easy to install, easy to use Resonant frequency (kHz): 4.6 +/- 0.5 KHz Resonant impedance (ohms): 300 max Note: Due to the difference between different monitors the picture may not reflect the actual color of the item