These diffusers are made from alumina that is heat-bonded. Use with 1/4" I.D. tubing. Available Sizes: # 1: 1" dia. x 2" Long, 3/16" outlet # 2: 1.25" dia. x 2.75" Long., 3/16" outlet # 3: 2" dia. x 4" Long, 3/16" / 3/8" outlet