We just learned about the Leading Wheel.
Another part of a steam locomotive is a Coupling, also called a coupler.
This is what connects the train cars to each other.
Some of the train couplings are loose with chains and bang into each other a lot.
Other types are very tightly linked together and don't move much.
![railway coupling](https://upload.wikimedia.org/wikipedia/commons/thumb/6/62/Railroad_coupler.agr2.jpg/483px-Railroad_coupler.agr2.jpg)
![railway coupling](https://upload.wikimedia.org/wikipedia/commons/thumb/6/6b/Carrage_couplings_on_ABT_Railway_%283939380014%29.jpg/450px-Carrage_couplings_on_ABT_Railway_%283939380014%29.jpg)
(from: wikipedia - railway coupling)
Kid Facts - Blast from the past: Valve Trim