Check the listing for details. Set of 2 8" Rubber Membrane Air Diffusers with 1/2" NPT Inlets. Condition: New. Listed at 40.84 USD. These EPDM rubber air diffusers are incredibly strong and are ideal for pond aeration, circulation and destratisfying applications. Unlike air stones these diffusers are easy to clean. Barbed inlets have multiple size barbs, simply cut to fit the size tubing you are using.