A ratchet-free and gear-free one-to-one mechanism for setting a dose in a syringe device comprising a dose setting member adapted to be rotated along a piston rod with a threaded outer surface so as to set a dose to be ejected.During dose setting the piston rod is locked such that rotational movement of the dose setting member does not result in rotational movement of the piston rod.During dose ejection the piston rod and the dose setting member are locked in relation to each other such that translational movement of the dose setting member causes relative rotational and translational movement of the piston rod.