3" - 54 mm centering ring holds 54mm motor tube inside 3" airframe. 1/4" plywood.
Fits into any 3" airframe. Works best with Rocketarium, Madcow kraft, GLR fiberglass, some LOC Paper 54mm motor tubes. (2.23-2.24" motor tube OD)

Please see next item for same ring cut for different 54 motor tubes