Mono Adaptor - Provides a safe and easy connection between 1 Maxi-Cosi car seat and the Bugaboo Donkey. Can be used in mono and duo configuration. Twin Adaptor - Provides a safe and easy connection between 2 Maxi-Cosi car seats and the Bugaboo Donkey. Can only be used in twin configuration. (only fits pre 2014 maxi cosi seats)