A drug delivery device , comprising: - a housing , - a plunger arranged within the housing , the plunger being movable along a longitudinal axis (X) and adapted to push a piston within a medicament container in a distal direction (D), the plunger being prevented from rotating and comprising an external thread , - a drive nut arranged within the housing , the drive nut comprising an internal thread engaging the external thread of the plunger , wherein an axial bearing is arranged between the drive nut and the housing to at least substantially prevent axial movement of the drive nut relative to the housing , - a mechanism configured to exert a force on the drive nut in the distal direction (D) through at least one rotatable component coupled to the drive nut for joint rotation and at least one non-rotatable component , wherein a bearing is arranged between the at least one rotatable component and the at least one non-rotatable component , the bearing having a smaller diameter than the axial bearing , wherein the at least one rotatable component comprises a drive sleeve arranged in the housing , wherein the drive nut and the drive sleeve are allowed to move axially relative to each other, wherein the drive sleeve is movable along the longitudinal axis (X) between a proximal position, in which the drive sleeve is prevented from rotating relative to the housing , and a distal position, in which the drive sleeve is allowed to rotate about the longitudinal axis (X), characterized in that the at least one rotatable component is coupled to the drive nut for joint rotation, wherein a drive spline between the drive sleeve and the drive nut couples the drive sleeve and the drive nut for joint rotation relative to the housing but allows for axial movement of the drive sleeve relative to the drive nut . - a housing , - a plunger arranged within the housing , the plunger being movable along a longitudinal axis (X) and adapted to push a piston within a medicament container in a distal direction (D), the plunger being prevented from rotating and comprising an external thread , - a drive nut arranged within the housing , the drive nut comprising an internal thread engaging the external thread of the plunger , wherein an axial bearing is arranged between the drive nut and the housing to at least substantially prevent axial movement of the drive nut relative to the housing , - a mechanism configured to exert a force on the drive nut in the distal direction (D) through at least one rotatable component coupled to the drive nut for joint rotation and at least one non-rotatable component , wherein a bearing is arranged between the at least one rotatable component and the at least one non-rotatable component , the bearing having a smaller diameter than the axial bearing , wherein the at least one rotatable component comprises a drive sleeve arranged in the housing , wherein the drive nut and the drive sleeve are allowed to move axially relative to each other, wherein the drive sleeve is movable along the longitudinal axis (X) between a proximal position, in which the drive sleeve is prevented from rotating relative to the housing , and a distal position, in which the drive sleeve is allowed to rotate about the longitudinal axis (X), characterized in that the at least one rotatable component is coupled to the drive nut for joint rotation, wherein a drive spline between the drive sleeve and the drive nut couples the drive sleeve and the drive nut for joint rotation relative to the housing but allows for axial movement of the drive sleeve relative to the drive nut . <EOS>