A kit for the assembly of a main door comprises at least two fixed uprights and at least one fixed crossbeam, associable with each other to define a fixed frame that can be attached to an access opening of a compartment, wherein the access opening has relevant reference dimensions; at least two movable uprights and a plurality of panels, associable with the movable uprights to define a movable leaf; a movement device/structure/component/element/unit/apparatus, associable between the movable uprights and the fixed frame; where at least one of the fixed uprights, the fixed crossbeam and the movable uprights is made according to respective predefined standard dimensions, which are bigger than the reference dimensions, and comprises at least one related trimmable portion, provided with at least one graduated reference scale adapted to allow the cutting of the trimmable portion depending on the reference dimensions.

A transmission assembly for converting a garage door operator (GDO) from a ceiling mounted configuration to a jackshaft configuration by operably coupling the transmission assembly to a motorhead configured to be employed in either the ceiling mounted configuration or the jackshaft configuration may include an output coupler to operably couple the transmission assembly to a drive tube rotatable to alternately open and close a sectional door, the output coupler comprising an output pinion, an input coupler to operably couple the transmission assembly to a motor output shaft of the motorhead, the input coupler comprising an input pinion, a flexible coupling member operably coupling the input pinion and the output pinion, a transmission housing configured to extend around at least a portion of each of the input pinion, the output pinion and the flexible coupling member, and a multi-position coupling bracket having a wall interface portion for rigid connection to a wall, a transmission interface portion to hold the transmission housing relative to the wall interface portion at a first selected angle, and a motorhead interface portion to operably couple the wall interface portion relative to the motorhead at a second selected angle.

A GDO conversion assembly for transitioning between a ceiling mounted and a jackshaft configuration includes a motorhead having a motor output shaft extending from a motorhead casing that includes a mounting interface disposed proximate to the motor output shaft, a track assembly including an input interface shaped to mate with the mounting interface to operably couple the motorhead to a sectional garage door, and a transmission assembly including an input coupler shaped to mate with the mounting interface to operably couple the motorhead to the sectional garage door. The transmission assembly includes an output coupler to operably couple the transmission assembly to a drive tube rotatable to alternately open and close the sectional door. The output coupler includes an output pinion. The input coupler includes an input pinion operably coupled to the output pinion via a flexible coupling member. The transmission assembly includes a transmission housing and a coupling bracket.