This adapter is a Schrader-to-Schrader connection designed to be able to connect to a valve in a tight corner. It is a friction fit by design, but for a better and easier seal, an 8mm OD O-ring can be pushed into the female end. The diameter of the female end is 12mm. I suggest printing it in PETG, or PC for strength.

Print Settings: infill 100% 0.16mm layers 0.5mm line width brim for adhesion no supports needed print at the highest practical temperature for the material used