>>7862724The bottom of a standard Duplo brick connects to a 4x4 Lego plate.
The bottom of a standard 2x2 Lego brick connects to the stud of a Duplo brick.
The connections are legal and snug. These engines require a specific configuration because they don't quite fit a 4x4 stud array on account of the molded sides, but a standard Duplo brick is easy to work with.
