A spacer unit inlet member integrally constructed of rigid or non-flexible material and capable of selectively mounting about its opening any one of a plurality of metered dose inhaler (MDI) actuators having different outlet size or shape. The inlet member includes a channel providing an opening of the inlet member and being formed by a wall substantially parallel to its rotational axis A peripheral edge of the wall is shaped substantially as a truncated oval. The inlet member further includes a pair of opposing curved walls surrounding and substantially parallel to the rotational axis of the channel and having an outermost edge comprising a substantially oval shape, and a wall substantially perpendicular to the rotational axis of the channel and positioned between the walls of the channel and the opposing curved walls.