Piezo discs are great for constructing pickups for acoustic instruments. Many users love them as the pickup in cigar box guitars, and they are a favorite amongst people experimenting with their acoustic instruments. These 50mm discs feature a brass plate, 0.1mm thick. Resonant Frequency 1.9KHz. Resonant Frequency, Resistance 1,000 ohm max. Capacitance 70,000pF +/- 30%.