This is a simple connector to join two 2-liter bottles together to make a Tornado Tube experiment for your kids. Fill one of the 2-liter bottles with water, connect, swirl, watch the tornado!Steve Spangler Science sells these on his website:http://www.stevespanglerscience.com/product/1226After making one for my sons instead, I decided that others needed this as well. :)You can see it in action here:http://www.youtube.com/watch?v=dv6vQU94wws&feature=player_embeddedIt is the simple colored connector that you see Steve screw onto the 2-liter bottles.Required items:While the o-rings aren't "required," I like to use them as it makes for a more water-tight seal.Instructions:Model notes:If you use the SCAD file to make alterations to this model, it also requires the "2LscrewPositive.11.stl" file from the "2 Liter bottle threads" thing found at http://www.thingiverse.com/thing:10489.Enjoy!Postscript:After publishing this, I found parkolay's "20_Oz_Bottle Adapter" http://www.thingiverse.com/thing:6090 that performs the same function. While they are very similar, mine will allow others to edit it via OpenSCAD. Also mine has a reducer in the center to make the tornado last longer while parkolay's does not.