Kit-of- parts, comprising: an outer post and an inner post that are rotationally locked and extendable relative to each other in a longitudinal direction, wherein the inner post comprises an external screw thread extending in the longitudinal direction; a nut configured to form a mating engagement with the external screw thread of the inner post and be driven along the external screw thread to selectively secure the inner post relative to the outer post in a drive mode; and a drive, comprising a drive housing accommodating a drive motor, and a connector configured to connect the drive housing with the nut and thereby connect the drive motor with a transmission, wherein the nut comprises: a housing; a rotatable member that is rotatably arranged in the housing, wherein said rotatable member comprises an internal screw thread that is configured to form a mating engagement with the external screw thread of the inner post; the transmission arranged in the housing and comprising an input shaft that is connectable to the drive, wherein said transmission is configured to selectively rotate the rotatable member relative to the housing in the drive mode wherein the transmission is driven by the drive, thereby also rotating the rotatable member relative to the external screw thread and moving the nut in the longitudinal direction along the external screw thread, wherein the nut is further configured to be moved manually along the external screw thread extending in the longitudinal direction in a manual mode, characterized in that the transmission is further configured to selectively form a coupling between the housing and the rotatable member in the manual mode wherein the nut is manually rotated relative to the external screw thread, the coupling causing the rotatable member and the housing to jointly rotate relative to the external screw thread, thereby moving the nut in the longitudinal direction along the external screw thread. an outer post and an inner post that are rotationally locked and extendable relative to each other in a longitudinal direction, wherein the inner post comprises an external screw thread extending in the longitudinal direction; a nut configured to form a mating engagement with the external screw thread of the inner post and be driven along the external screw thread to selectively secure the inner post relative to the outer post in a drive mode; and a drive, comprising a drive housing accommodating a drive motor, and a connector configured to connect the drive housing with the nut and thereby connect the drive motor with a transmission, wherein the nut comprises: a housing; a rotatable member that is rotatably arranged in the housing, wherein said rotatable member comprises an internal screw thread that is configured to form a mating engagement with the external screw thread of the inner post; the transmission arranged in the housing and comprising an input shaft that is connectable to the drive, wherein said transmission is configured to selectively rotate the rotatable member relative to the housing in the drive mode wherein the transmission is driven by the drive, thereby also rotating the rotatable member relative to the external screw thread and moving the nut in the longitudinal direction along the external screw thread, a housing; a rotatable member that is rotatably arranged in the housing, wherein said rotatable member comprises an internal screw thread that is configured to form a mating engagement with the external screw thread of the inner post; the transmission arranged in the housing and comprising an input shaft that is connectable to the drive, wherein said transmission is configured to selectively rotate the rotatable member relative to the housing in the drive mode wherein the transmission is driven by the drive, thereby also rotating the rotatable member relative to the external screw thread and moving the nut in the longitudinal direction along the external screw thread, wherein the nut is further configured to be moved manually along the external screw thread extending in the longitudinal direction in a manual mode, characterized in that the transmission is further configured to selectively form a coupling between the housing and the rotatable member in the manual mode wherein the nut is manually rotated relative to the external screw thread, the coupling causing the rotatable member and the housing to jointly rotate relative to the external screw thread, thereby moving the nut in the longitudinal direction along the external screw thread.