Roughly based on a swedish ore care. They are always used as pairs. To be used with Micro-Trains Roller Bearing trucks. May need some work to fit the trucks properly. Designed for "White Strong & Flexible" so long trains don't eat too much into the budget. There is space to put some weight in below the basket. Update: The placement of the vertical gizmos in the first version was incorrect. Instead of both on one car, each car should have one. This is fixed now. Thanks for pointing it out!