The twin extension set is used to extend your bugaboo donkey duo stroller into bugaboo donkey twin stroller. The twin extension set is sold separately and is not included in the bugaboo donkey mono or bugaboo donkey duo. To complete the twin extension set, please add a bugaboo donkey tailored fabric set in the color of your choice. This extension set is compatible with the bugaboo donkey tailored fabric set and bugaboo donkey breezy sun canopy.