Put one of these caps on the end of a Boomwhacker tube and you'll lower the tone by a full octave! Play the tubes as usual or hold them vertically and tap on the floor as a stamping tube. Place on the higher-octave Boomwhacker tubes to create the same tones as the bass octave tubes. Place on the bass octave tubes, and take your Boomwhackers down another octave, making a 3-octave range possible. Set of 8.