A piezo disc epoxy potted in a tough 3D printed enclosure with a strong magnet and strain relief microphone cable in a choice of lengths. Designed with external field recording in mind, for amplifying metal structures such as bridges, masts, gates or any other ferrous metal source. Piezos are only really useful when firmly held in place, and the magnet in this assembly does just that, leaving your hands free to tend to recording equipment and/or unleash your inner percussionist on metal things. A great sound design tool.