These O2 Cylinder Stones accelerate oxygen replenishment and increase water circulation when used with a high-output air pump. The 4” O2 Cylinder Stone has a 2” diameter and is compatible with 3/16” ID tubing. These are large stones, and they put out a ton of air. It is important that you have a capable air pump, like one of our commercial pumps, in order to get the most out of these great air stones.These great quality Air Stones aerate and add oxygen to the water in your reservoir or grow system. Circulates nutrients into the water and helps to maintain an even water temperature. Use with 3/16 in ID air line product