WATER TIGHT Rubber Grommets: in connections of DIY hydroponic systems, dutch buckets, dripping systems, siphon aquaponic systems and irrigation systems… LEAK-FREE SEAL: Donut-shaped Rubber Grommets help transfer water or nutrient solution from one reservoir to another one with tubing and barded fittings or piping and 3/4 Inch Vinyl Tubing DURABLE: periodically replace worn old ones in existing hydroponic systems to ensure air and water tight seals in your hydroponic systems 3/4 inch Donut Rubber Grommet also goes with SCH40 1/2 inch PVC pipes or pipe's outer diameter matches grommet's inner diamete The inner diameter of rubber grommet is 1” but the drilled hole on the bucket it fits into will need to be 1-3/8 inch