The flow restrictor is designed to fit tightly right inside semi-rigid 1/4 inch RO tubing. If your RO reactor use soft air tubing, then you have to modified it as needed. I modified mine 10+ years ago. I used soft black air tubing and use a nipple attachment my fitting is slightly different. Anyway, once you know what you need to do to deliver the fine stream of CO2 bubbles to your reactor, you just have to use your judgment to determine the best way to do it.