Screws on to bottle like a bottle cap and ensures that the water drips at a slow but steady rate. To attach to the next bottle, thread zip ties through the four holes. Fits 3/8-inch tubing (if you’re using tubing to transport the water to the plants). Visit our website (https://www.3dponics.com) and join our Google+ community (https://plus.google.com/u/0/communities/111638904033818784260) to take 3Dponics to the next level! Want to print this part? Search today's top 3D-printing services and materials to find the cheapest price for your project. Go to https://www.3Dprintler.com3D Printing Settings: -Low quality; 0.2 mm; 2 shells; 10% infill Tested on MakerBot, Ultimaker, M3D Micro and Formlabs