Abstract: A fitting is provided for mounting a metered dose inhaler and adapter on the entering upstream end of a cylindrical aerosolization spacer. The fitting includes a cylindrical portion mounting on the cylindrical wall of said aerosolization spacer, and further includes a transverse wall having therein a centrally disposed opening having an oval shape truncated at the ends. The opening is reinforced by radially disposed ribs having inner longitudinal edges, which with the edge of the truncated oval opening comprises the sole structure of the fitting engages the mouthpiece of a metered dose inhaler adapter. A non-leaking fit between the adapter and the fitting is produced notwithstanding the shape of a particular metered dose inhaler adapter mouthpiece, such as truncated oval, oval, or circular.