Simply the best air stone available on the market today. This micro pore oxygen diffuser produces an average bubble size of .09 to .25mm, much smaller than cheaper air stones. Smaller, more frequent bubbles means better absorption to produce the most oxygen rich nutrient solution possible. This double diffuser features two 5.25” fire kilned ceramic air stones connected with a red tee manifold. Th double XL features two 10" stones of equal diameter and quality. Both include adapters for 3/8" and 1/8" air line. Made in the USA.