UPPAbaby Vista Upper AdaptersThe Vista Upper Adapters are required when using your Vista (2015 Current Model) stroller in duo configuration with the Vista Bassinet (2015 Current Models) Vista Toddler Seat, or Mesa Infant Car Seat (sold separately). These adapters provide additional space between the primary and secondary seats. Specifications Quick, no tools attachment When used for the toddler seat creates more space between the upper and lower seat, so kids are farther apart.