A screw and guide rail coupling assembly (11) is for a garage door operator (10). The garage door operator (10) has a motor-driven rotatable screw (20) at least partially within a nonrotatable guide rail (26) and a slide (29) guided by the guide rail (26) and movable longitudinally therealong by engagement with the screw (20) and connectable to open and close the garage door (114). The screw (20) is in at least first and second screw parts (37,38), and a screw coupling (42) is adapted to interconnect adjacent ends of the first and second screw parts (37,38). The guide rail (26) is in at least first and second guide parts (39,40), and a guide coupling (43) adapted to interconnect adjacent ends of the first and second guide parts (39,40). The screw coupling (42) is longitudinally spaced or offset from the guide coupling (43) wherein the screw coupling (42) is completely contained and supported within one of said first and second guide parts (39,40). The offset provides a significant increase in the maximum torque of the screw and guide rail coupling assembly (11).