The model rocket centering ring is the part of the model rocket engine mount kit that keeps the engine tube centered in the body tube of the model rocket. These are the two disk shaped rings in the picture to the right.

Another function of the centering ring is to provide an air-tight seal of the rocket engine end of the model rocket. This is required to allow the rocket engine ejection charge to deploy the recovery system. If the centering rings were not air tight, the ejection charge would not have enough force to push out the nose cone and recovery system.