The Classic Balance Ball Leg Extenders add 2″ of height to help you sit more comfortably and with correct posture. Easy to install; no tools necessary. These extenders change the suggested height range up to 6’1″. Adds 2″ of height to your ball chair Helps you sit more comfortably and with better posture Extends the height range to 6’1″ Set of 4 Easy to install Compatibility: Classic Balance Ball Chair and Backless Balance Ball Chair. These extenders are NOT compatible with the Ultimate Balance Ball chair, Custom Fit Chair or Stools.