Recommended air flow" 3.0 - 4.2CFM. Dimensions: 12" x 21" underlayment. 1/2" barbed inlet. Includes check valve to prevent water from filling air line when not in use. Polyethylene underlay keep diffusers from settling into the mud and prevents sediment erosion during operation. Standard air diffusers are 6"long, standard airline connection is for 1/2"poly tubing. Includes 6 air stones.