The audio jack cover is a rubber plug that prevents water and dust from entering the headset jack when not in use. A short tether prevents the cover from being misplaced when a headset is in use. Please note that the Audio Jack Cover is not required to keep the unit sealed against dust & water. Rather, it is intended to keep dust, mud and snow from accumulating in the jack. This is a standard accessory included with each Ranger 3 computer. It is a consumable accessory that can wear out in normal usage.