4.0" - 1.1" (4" - 29 mm) centering ring holds 29mm motor tube inside 4" airframe. 1/4" plywood.
Fits into any 4" airframe. Works best with Apogee, LOC Precision, Madcow Paper. (1.215" motor tube OD)

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