This is a spray head to hold Mentos and drop them into a bottle of Diet Coke.
This is based on LT1Pat's great work on the pop bottle threads; I rebuilt it short enough to fit my Emaker and made the spray head integral, with internal slopes steep enough to print without needing support in the middle.
I just updated the files to get the jet centered and add some material to the outside of the threaded area.
Print this at 100% fill. FYI, it leaks out of all the stops and starts if your filament diameter/retract isn't well tuned! Try both no extra shells and 2 extra shells to see which gives you a better thread. Even a poorly printed thread will screw on and work just fine; just scrape off the excess strings. Partially straighten a paperclip, leaving a loop. Tie a long string onto the loop. Drop in your Mentos, stick in the paperclip, and screw it onto the Diet Coke bottle. Step back (if you want to stay dry), and pull the paperclip out!