My HobbyLinc order arrived fast (in 5 days even with HAZMAT) and I used one of the Estes 24mm PVC retainers even faster. I cut and ground out the bottom centering ring, added a new foamboard ring and the retainer, as shown below. Ignore the ugly glue marks. This rocket has been repaired many times, both when it was mine and before. One day I might repaint the lower part.