A dose adjustment mechanism (4) for a drug delivery device (1), said mechanism comprising: an internal housing (300) having a first helical groove (302), which preferably is a male helical groove, along along an outer surface (304) of said inner housing (300), said inner housing (300) comprising a first rotation stop member (306) near one end of said helical groove (302)； and a selection sleeve (10), preferably a single molded component, rotatably engaged with said helical groove (302) of said internal housing (300), which preferably is a male helical groove, said selection sleeve (10) comprises preferably a generally smooth outer surface (410), wherein said selection sleeve (10) comprises an inner surface (404) having a second helical groove (402) and a second rotation stop member (406)； wherein said first rotation stop member (306) comprises means preventing a user from selecting a dose greater than a predefined maximum selectable dose when said user rotates said selection sleeve (10) to select a dose, wherein said first rotation stop member (306) of said internal housing (300) engages with said second rotation stop member (406) of said selection sleeve (10) when a user attempts to select a dose greater than said selectable dose predefined maximum； characterized in that said second rotation stop element (406) comprises a flexible element (408) and said first rotation stop element (306) is housed in a flexible arm element.Un mecanismo de ajuste de dosis (4) para un dispositivo de administración de fármacos (1), comprendiendo dicho mecanismo: un alojamiento interno (300) que tiene una primera ranura helicoidal (302), que preferiblemente es una ranura helicoidal macho, a lo largo de una superficie externa (304) de dicho alojamiento interno (300), comprendiendo dicho alojamiento interno (300) un primer elemento de tope de rotación (306) cerca de un extremo de dicha ranura helicoidal (302)； y un manguito de selección (10), preferiblemente un único componente moldeado,
