4.0" - 3" (4" - 75 mm) centering ring holds 75mm motor tube inside 4" airframe. 1/4" plywood.
Fits into any 4" airframe. Works best with Madcow paper, Performance Rocketry fiberglass, Quantum tubing 75mm tubes. (3.0 - 3.12" motor tube OD)

Please see next item for same ring cut for different 3" (75mm) tubes.