From Thule, this stroller features: Upper and lower adapters to configure your Thule Sleek into a sibling stroller Quick and easy mounting and dismounting Adapters can be kept on while folding stroller Enables duo configurations with Thule Sleek main seat, Thule Sleek Sibling Seat, Thule Sleek Bassinet and specific car seats (for car seat configurations additional car seat adapters are required) Thule Sleek Adapter kit is included in Thule Sleek Bassinet and Thule Sleek Sibling Seat Imported.