Cylindrical shaped air stone. Great way to aerate and circulate nutrients. 0.25 in. fitting. Available in small, medium and large sizes. About Hydrofarm, Inc. Celebrated as the nation's oldest and largest manufacturer of hydroponic equipment and grow lights, Hydrofarm has made professional-grade equipment available to all since 1977. All grow lights and electric components are UL listed, unlike many competitor products, meaning you get years of reliable and safe use out your high-intensity lights. All products are covered by a one year warranty, at the least. In some cases Hydrofarm ensures the performance of their products for five years. Size: Small.