Step-by-step advance mechanism, especially for hand-held devices (1) intended to dispense portions of inhalation medicaments, comprising an annular housing around whose longitudinal axis (xx) a scale ring (27) rotates, moved step by step, induced to this, by advancing fingers which, during the drive stroke, swing against an elastic request in the direction of a plane perpendicular to the longitudinal axis (xx) of the housing (34) and thus cause the rotation of the scale ring to through a toothed, characterized in that an annular part (17) arranged in rotation in rotation in the housing (34) has at least one groove (19) that starts obliquely upwards from the lower edge and is intended to allow the entry of a guide pin (33) of a stepper step finger star (S), whose stepper step fingers (28) directed obliquely upward in the direction of secant form from a hub central (29) are introduced during the drive stroke, tilting inwards against its own elastic tension, in the teeth (21) to rotate the scale ring (26).Mecanismo de avance paso a paso, especialmente para aparatos manuales (1) destinados a dispensar porciones de medicamentos de inhalación, que comprende una carcasa anular alrededor de cuyo eje longitudinal (x-x) gira un anillo de escala (27) movido paso a paso, inducido a ello por unos dedos de avance que, durante la carrera de accionamiento, basculan en contra de una solicitación elástica en dirección a un plano perpendicular al eje longitudinal (x-x) de la carcasa (34) y ocasionan así el giro del anillo de escala a través de un dentado, caracterizado por que una parte anular (17) dispuesta solidariamente en rotación en la carcasa (34) presenta al menos una hendidura (19) que parte oblicuamente hacia arriba desde el borde inferior y está destinada a permitir la entrada de una espiga de guía (33) de una estrella de dedos de avance paso a paso (S), cuyos dedos de avance paso a paso (28) dirigidos oblicuamente hacia arriba en sentidos contrarios en forma de secante desd
