24 inch (61 cm) length, 304 L or 316 L stainless steel, open or closed bottomStandard oxygen transfer efficiency of approximately 1.0% per foot of submergence* * Diffuser performance is calculated for each specific application based on flux, density, depth and several other parameters. Please contact an Aqua-Aerobic Systems, Inc. representative for your application. Test results per ASCE testing methods are available.