Centering rings are used to put a tube in the middle of another. This is most common for motor sections, where the motor diameter is often smaller than the diameter of the rocket body itself. Centering rings are not usually strong structural elements on their own - usually the fins will be bonded to the tube in the middle of the centering rings. They can be drilled into for motor retention purposes, as shown below: (PICTURE OF SCREW-WASHER RETENTION)
Only 2 rings are necessary to center a tube, but often 3, or even 4 will be used for longer inner tubes.
Thrust rings
Thrust rings are load-bearing centering rings at the bottom of a motor section. They transmit the thrust load to the rest of the rocket. It is important to make sure that these are either:
- Bonded to the fins, which would be bonded to the motor mount tube,
- Attached such that the ring extends over the bottom of the motor section tube, and/or
- Is significantly thicker than the rest of the centering ring(s).