... , AS, B, BS, C, CS, D, DS, E, ES Air Vent HeadAir Vent Head can be used on water tank ... JIS-KS91A-121, CB/T3594-94, DIN, ISONote:Oil Tank Air Vent head has character of cover on top of head ... .Water Tank Air Vent head has character of permeability on two side ... used in ballast bilge. We have many choice of Air vent head, please contact me for more products information