Adjustable Sizes: Fitbit inspire hr strap small size fits 5.5"-7.1" wrists. Fitbit Inspire hr strap large size fits 7.1"-8.7" wrists. You can adjust the strap to fit your wrist easily. For Fitbit. Sweat resistant & Water resistant: No worry about losing your Inspire - Locks onto Fitbit Inspire/Inspire HR/Ace 2 watch interface precisely and securely.