StratoFins Screw-on Water Rocket Fins + Rubber Stopper Launcher Compatible with 95% of all available launchers either homemade or commercially available. Works with various styles: cable ties, rubber stopper, expanding tube, nozzle, or O-ring. No tools or glue required for assembly, simply screw-on to a 2 liter soda bottle or smaller. Take your water rocketry to the next level of higher flights with screw-on StratoFins. StratoFins Plus kit includes 1 ring, 3 fins, 1 rubber stopper launcher along with an instruction sheet.