coupler to screw two PET bottles together. Good for making funnels, hourglasses, or tornado demonstrations. The PET bottles I'm referring to are the common bottles for 2 liter soda. The same top seems to be used on other sizes of soda bottles too. Full OpenSCAD souce included. Many objects are in the file. The coupler module is the one featured in this "thing". The most critical piece of source is the "PETtap()" module, which taps threads for PET bottle tops. I will post "thing" entries for water rocket nozzles, and dog bowl fillers as they are printed and tested.