Tuning plates are designed to send the heat under the grill grates and distribute it evenly across the cook chamber.

This is often useful when you have a cooker full of meat and require a more even temperature left to right. 

It also enables you to build a bigger fire, as the heat is controlled and sent under the food instead of over it.

These are mild steel and require a layer of cooking oil to prevent from rust.

These can also be used as a reverse flow plate for all cactus jack models that have this feature,