A simple tool to demonstrate rotational inertia to student.  The steel ring and wooden disc are of identical diameter and identical mass. Their inertia is the same, but not their rotational inertia, due to the fact that the mass is distributed differently in each of the two objects.

Roll them down an inclined plane. Which will reach the bottom first? What happens if you let them keep moving?

Diameter of each object: 106mm.
Width of each object: 18mm.