Made this quick adapter for my new Reedin Kite, as it uses a non-standard 31mm inlet.
This screws directly into the pipe of the Decathlon pump, not sure what the kind is, but the inner diameter of the adapter is 20mm, I think that it's the same kind that Slingshot uses for their Kites.
Printed in PETG, I had to adjust the outer diameter to get it perfect, you might have to adjust it depending on your printer's tolerances, I included the Fusion 360 file.
The author marked this model as their own original creation.