A centring drum for filter assembly machines, the centring drum having external axial seats movable with the centring drum about a longitudinal axis of rotation, and for receiving respective double filters, at least some of which are offset laterally, along the relative seats, with respect to a central transverse reference plane; each seat housing a respective stop member movable with the relative seat about the longitudinal axis of rotation, and located on a respective side of the reference plane to define a centred position of the relative double filter, and a push device for moving the relative double filter axially onto the relative stop member; the stop members defining a first and a second succession of stop members, which are located on opposite sides of the reference plane and are both connected to a position adjusting device movable about the longitudinal axis of rotation and for moving the two successions equally and oppositely along the longitudinal axis of rotation.