A female connecting device used to accept a male helium/oxygen connector to connect two devices together to provide a continuous passageway for the delivery of a mixture of 79% helium (He) and 21% oxygen (O2). It has safety features such as a specific mechanical mating pattern, colour coding and a dedicated tube diameter connection to prevent wrong connection and allows a user to rapidly connect and disconnect helium/oxygen dependent devices. It can be attached, e.g., to a regulator or an extension tubing. It can be designed as a diameter-indexed safety system (DISS) connector or a non-interchangeable screw-threaded (NIST) connector. This is not a helium/oxygen terminal unit.