Diameter: accomodates 21.8 mm through 32mm (children through adult)
Mounting position: securely holds speaker at any angle (even upside down). Can be mounted in vertical position on handlebars as on some beach cruisers and BMX style bikes.
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Power: 3 AAA batteries (not included). Speaker can also be powered with a 4.5 volt USB power cable (not included) if connecting to a laptop.