A spring assisted drug delivery device (80, 90, 100) is provided comprising a housing (4) and a lead screw (22) having a longitudinal axis, a distal end and a proximal end that is rotatably fixed during dose setting and dose delivery and axially moveable in a distal direction relative to the housing. The device further comprises a drive nut (23) threadedly engaged and screwable along the lead screw threaded shaft and a number sleeve (24) threadedly engaged with the housing (4) to be screwable relative to the housing (4). A dial link (25) is connected with the drive nut (23) and axially moveable and rotatably fixed relative to the drive nut (23) and an inner sleeve (29) is threadedly engaged with the number sleeve (24), the inner sleeve (2) being axially moveable and rotatably fixed relative to the housing (4). A mid-body (20) is axially fixed inside of the housing (4). A spring (82, 92, 102) is provided that assists a user of the device during a dose administration step.Se proporciona un dispositivo de administración de fármacos asistido por resorte (80, 90, 100) que comprende un alojamiento (4) y un husillo (22) que tiene un eje longitudinal, un extremo distal y un extremo proximal que está rotatoriamente fijo durante el establecimiento de dosis y administración de dosis y axialmente movible en un sentido distal respecto al alojamiento. El dispositivo comprende además una tuerca de impulso (23) acoplada de manera roscada y enroscable a lo largo del vástago roscado del husillo y un manguito de números (24) acoplado de manera roscada con el alojamiento (4) para ser enroscable respecto al alojamiento (4). Un enlace graduador (25) se conecta con la tuerca de impulso (23) y es axialmente movible y rotatoriamente fijo respecto a la tuerca de impulso (23) y un manguito interior (29) se acopla de manera roscada con el manguito de números (24), siendo el manguito interior (2) axialmente movible y rotatoriamente fijo respecto al alojamiento (4). Un cuerpo medio (20) está axi
