FAUCET AERATOR ADAPTER

My neighbour wanted to fit a water cooler takeoff to their laundry sink.

This adapter has a couple of odd threads - the inner is M16.5 x 1.25  the outer M21.4 x1 - I presume that my metric measurements are close to some other weird plumbing kind - but with a 1mm thick O-ring at each end they work very well.

I printed the one shown in Prusament Jet Black PETG at 1.5mm STRUCTURAL settings, no supports are necessary.