Cluster centering ring, fits 4.0" airframe. (3) 29mm (1.1") holes. 3/16" birch plywood.
Fits into any 4" airframe. Works best with LOC Paper, PML and GLR phenolic, Hawk Mt and Performance Rocketry fiberglass 29mm motor tube. (1.269" motor tube OD)

Please see previous item for same ring cut for different 29mm tubes.