This adapter adapts a 38mm 2-start PET bottle thread to a 38mm 3-start thread.
This is often necessary because there are PET bottles with different threads and most models are designed for 38mm PET bottles with a 3-start thread.
The model was specifically designed to mount existing bottles to a birdfeeder.
The 3D model can be printed without supports if the external thread points towards the printing plate.
The author marked this model as their own original creation.