This sleeve will fit the Jawbone UP or UP24 fitness wristband and connects holds the two ends together to prevent the band from falling off or gettings damaged. It features rounded edges for comfort and i recommend a smooth or polished material surface to avoid chafing. To use just place wristband on wrist then slide over one endand open wristband enough to slide other end inside. This will not work iuf your wearing a wristband that is too small and tight because that causes the wristband to bulge and will not allow it to lay flat. If you can press your band ends flat against your skin when it is on this will fit you. This is also available for customization through custommaker but i have not tested that feature so i cant comment on its use.