Harmonica players who play the instrument while performing on another instrument with their hands (e.g., an acoustic guitar) often use an accessory called a neck rack or harmonica holder to position the instrument in front of their mouth. A harmonica holder clamps the harmonica between two metal brackets, which are attached to a curved loop of metal that rests on the shoulders. The original harmonica racks were made from wire or coat hangers. Models of harmonica racks vary widely by quality and ease of use, and it quite often takes experimenting with more than one model of harmonica rack to find one that feels suitable for each individual player. This device is used by folk musicians, one-man bands and singer-songwriters such as Bob Dylan, Tom Harmon, Neil Young, Eddie Vedder, Bruce Springsteen and blues singers Jimmy Reed and John Hammond Jr. The HarpArm is a magnetic harmonica holder that attaches to standard straight or boom microphone stands. (source)