Science Notes(ball and ring experiment)

Why is the metal ball able to pass through the metal ring after heating the ring?

When the ring is heated,it expands in size and the ball which is still the same size as before is able to pass through the expanded metal ring.

I had this question in my mind after watching and learning the ball and ring experiment.When you heat the ring,does it mean that the whole ring expands or just the hole on the middle that expands.My guess is that the whole ring expands as it cannot be the hole that only expands.If only the hole expands,then the proportionate of the hole to the whole ring is wrong.Also,when you heat up the ring,th whole ring gains heat and not only the ring.that is how I came to the conclusion tha when you heat up the ring,it is the whole ring that expands and not only the hole in the middle of the ring.