O A garage door actuator (10) comprises a motor-driven screw (20) at least partially disposed within guide means (28) and a partial nut (30) which is guided by the guide means and moved longitudinally therealong by engagement with the rotating screw. The partial nut (30) is connectable to a garage door to open and close the door. In order to shorten the package in which .the garage door actuator is transported or shipped, the screw and guide means are both formed in two or more parts which can be coupled together by a screw coupling (11). The screw parts (21, 22) are shipped to the customer in a disconnected condition but one in which the coupling readily may be connected in a proper phase to avoid mismatch of the screwthreads.