This 3D model are parts for the Quest Courier model rocket. They can be used to replace missing parts or to scratch-build one or make an upscale of it. This model rocket that's designed to carry an egg (or other things) in its payload bay. It uses 18mm (A through C) motors. I have included a version of the nose cone and the fin cans that will fit Estes BT-55 tubing.

https://www.thingiverse.com/thing:5200257