I designed this adapter to be able to blow out dusty or dirty air lines using a “safety” compressed air nozzle that has pressure relief holes which prevents it from mating up with the tube. The air nozzle opening is about 12.5mm and the tube opening is tapered to fit tubing from 4mm to 8mm OD. I printed it with TPU so it's flexible enough to fit different nozzles so long as they're close to the right size. Both ends are just a friction fit as it's not really meant to hold much pressure. Softer TPU will allow for more “stretch" but isn't necessary, I've printed successfully with both 98A and 95A TPU. There's a pocket clip but don't count on it holding very tightly, I use it to hang it on the edge of a pocket in my tool bag. There's also a small hole for a keyring or lanyard.

(The imprinted text on the side reads: For Maintenance Use Only)