Features: 1. [High Quality] Made of brass and ceramic, temperature resistant, stable, durable and long service life. 2. [Size] Piezo pickup plate with thickness in 0.4mm, small, thin and lightweight. 3. [High Performance] Resonant frequency 4.6 '/- 0.5 KHz, resonant impedance 300 ohms max, low power consumption and high sensitivity. 4. [Easy To Use] These pre-wired piezo pickups are easy to install and use in cigar box guitars, foot stompers and other home-made instruments for sound and vibration detection. 5. [Wide Usage] Perfect for beginner to use as touch-sensors, electronic drum triggers, buzzers, make your own contact mics, also used for watches, cameras, phones, electronic toys, computer, etc. Specifications: Type: 20mm diameter & 250mm cord length / 27mm diameter & 330mm cord length / 35mm diameter & 250mm cord length (Optional) Material: Brass Thickness: 0.4mm thick Resonant Frequency: 4.6 ± 0.5 KHz Resonant Impedance: 300Ω max Package Weight: 50g/70g/70g Package Size: 15*10*5cm Package List: 15*Piezo Discs