A retainer for a single-sided modular cannula portable gas delivery system to secure a mouthpiece or nosepiece, a gas delivery pack and a single-sided modular medical cannula tubing assembly. An over-the ear secured modular mounting sleeve having an elongated central semi-circular cavity for securing a nasal cannula. A pair of engaged discs allow the cavity to rotate. The pair of discs have a plurality of elevated ridges that lock the semi-circular cavity in angular relationship to the ear piece. The ear piece has a malleable metal insert that is located at least partially within the ear piece that allows the ear piece to be bent for comfort.