Bogie

framework which carries a wheelset and is attached to a rail vehicle

A bogie (called a truck in North American English) is a chassis, with wheels, attached to a rail vehicle, such as a boxcar. A bogie usually has four or six wheels. Each rail vehicle has a pair of bogies. The bogies can turn slightly to allow the rail vehicle to pass easily around curves in the railway track.

A bogie detached from a railway wagon