This is an extension to the portafilter holder: https://www.printables.com/de/model/296316-portafilter-holder-for-baratza-encore
The adapter ring makes the portafilter stay inside the holder without using a hand.
The height is 12mm. This fits a Gaggia Classic Portafilter perfectly.
Simply glue to the walls of the portafilter holder.
I uploaded as STEP-file: You can customize the height to fit your needs.
The author remixed this model.