This is a pack of 1 piezoelectric elements, pre-wired with leads to save you having to solder the leads on yourself. 50mm is a perfect 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. An electric pick-up is a sure-fire way to take your cigar box guitar or another build to the NEXT LEVEL, and many builders report that their instruments are much more attractive to potential buyers if they include a pickup.