Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:5264755.

66mm to 55mm Model Rocket transition that was made for cardboard tubes. The shoulder sizes are different due to the original requirements of the model. I used 4 walls to fill in the walls which seemed to work well when tested many times. The PLA survived the ejection charges well with no problem and received little to no damage when landing, just a little dirt.