(Fits PetStop® and DogWatch™ Receivers) X-Small – Adjusts 8”-11” and ¾” wide Small – Adjusts 10”-13” and ¾” wide Medium – Adjusts 13”-17” and 1” wide (pink is ¾” wide) Large – Adjusts 17”-23” and 1” wide (pink is ¾” wide) X-Large – Adjusts 23”-31” and 1” wide Note: Pink and Purple are not available in X-Large