4" - 38mm (99 - 38mm) centering ring holds 38mm motor tube inside 4" airframe. 1/4" plywood.

Fits into any 4" airframe. Works best with Rocketarium 38mm (S), LOC and Madcow 38mm Cardboard Tube, Blue Tube (41.6mm motor tube OD)

- 41.6, - 98.9mm,  6mm,  24g