A threaded rod for an injection device, wherein the rod includes a thread on an external surface, the thread supporting or carrying, at least partially, engaging elements and/or teeth. In one embodiment, the present invention encompasses a dosing mechanism for an injection device, including a rotational defining element which enables a threaded rod to be rotated in one direction, rotation being blocked or prevented in the counter direction by at least one blocking element which co-operates with a thread of the threaded rod, wherein the thread carries, supports or has associated teeth and/or engaging elements. In one embodiment, the present invention encompasses an injection device including at least one engaging element which co-operates with a blocking element associated with a threaded rod, whereby the threaded rod is rotatable in one direction in relation to the injection device, rotation in the opposite direction being prevented.