This is a nice entry-level pack of 3 high-quality piezos, pre-wired with leads to save you having to solder the leads on yourself. 27mm is a great size for installing in cigar box guitars, foot stompers and other home-made instruments. They can also be used for custom pickup arrangements in more traditional stringed and percussion instruments. Some builders claim that the larger-diameter piezos respond better to bass tones, others claim that the size of the piezo doesnt really matter. Try several sizes and see for yourself! An electric pick-up is a sure-fire way to take your cigar box guitar or other homemade instrument to the NEXT LEVEL, and many builders report that their instruments are much more attractive to potential buyers if they include a pickup. So here is your chance to take the plunge without dropping a huge wad of cash! Technical Specs: Plate Diameter: 27mm (1.06 inches) Element Diameter: 20mm (.787 inches) Plate Thickness: .54mm (.021 inches) Lead Length: ~50mm (1.96 inches) Plate Material: Brass Resonant Frequency (kHz): 4.6 +/- 0.5kHz Resonant Impedence (ohm): 300 max. Capacitance (nF): 20.0 +/- 30% [1kHz]