The present invention relates to a millable plugging device for use in a well pipe. The device includes an inner mandrel and an outer housing provided radially outside at least parts of the inner mandrel. A sealing assembly is provided radially outside the inner mandrel, where the sealing assembly is configured to be brought from a run state to a set state by a relative axial displacement between the inner mandrel and the outer housing. The millable plugging device has a first center axis and the second mandrel section has a second center axis which is displaced parallel in relation to the first center axis. Rotation of the inner mandrel in the set state is bringing a third mandrel section of the mandrel to a locked state, in which further rotation of the inner mandrel is prevented.