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 PML and GLR phenolic, Hawk Mt and Performance Rocketry fiberglass, LOC paper, semroc paper 75mm motor tube. (3.15 - 3.25" motor tube OD)

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