The Stax Plug Caps fit over the male Stax headphone or extension cable termination to protect the protruding pins. It's a nice little piece of kit that provides peace of mind for those like me who worry about damaging their non-removable headphone cable. Inexpensive yet a powerful tool for us who feel compelled to worry about such things. And the Zepp Crew are a delight to order from, always friendly and helpful. Thank you Zepp Crew!