This is the male fitting for a standard garden water hose quick connect.
To make things easier in the garden, I use garden hose quick connectors. I bought enough of the female connectors for all of our spigots and hose ends, and I bought enough male connectors for all of the garden hoses and the three or four sprayers, sprinklers, and other water tools we had at the time.
I keep having to buy new male connectors whenever we get additional water hose attachments; the power washer, a slip-and-slide, and other things. I don't want to have to keep swapping the fitting from one accessory to another when I need to use it. If I do that, then what is the point of having quick connects. Running to the store every time was equally as frustrating, so made one I can print on an as needed basis.
It works better than I expected, honestly. I printed it in ABS with 20% infill and a 4mm brim. I printed it in the provided orientation, with the quick connect pointed down and the thread end up. I did use supports, since I didn't think the hex flange would bridge very well. I recommend printing in this orientation so the supports do not foul the threads. I am sure you can see in the picture where the support connected to the flange, and it does not leave a smooth surface.
I included pictures of the brass fitting as well, to show you what type of quick connect this piece fits. This is the only type of quick connect that I have come across, but just in case there are others out there, you have a reference.