64mm pipe adapter for Dalap air inlet

The Dalap 3163 air inlet (see https://dalap.eu/distribution-elements/164-2971-pvc-disc-valves manufacturer site) is designed for pipes with internal diameter of 80mm, however, many heat recovery ventilation systems use pipes of 64mm internal diameter. This inlet could suit them very well if the neck would be longer and wouldn't need the steel springs at all to fit inside.

This adapter (in two heights) is to replace the steel springs and extend the neck of the inlet so that it not too tightly, but gently fits into the pipe. Remove the steel parts, and put this adapter on top using the original screws. Stays firmly in the pipe looking down from the ceiling.
Designed in FreeCAD.