A print liquid supply interface structure is provided, to fluidically connect a fluid supply container to a receiving station, comprising a liquid channel having at least one liquid channel wall, the liquid channel including a liquid interface, and at least one key pen next and parallel to the needle receiving portion of the liquid channel, protruding from a base over more than 10 millimeters. In another example a key pen structure is provided. In yet another example an interface structure for receiving a separate key pen is provided.