Specifications:Can prevent the aquarium from the water flowing back, which is caused by the decrease of CO2 pressure,and keep the function and service life of CO2 bottle.When used in the ozone generator, it can prevent the ozone from flowing back to the air pump and eroding the propeller.It can protect the power head from the water flowing back which is caused by power cut.Fits standard aquarium CO2 pipe(4mm) internal diameter.Type: Carbon Dioxide Check ValveMaterial: Stainless SteelFeatures: Durable, Easy to Use, CO2 Regulator, One-way DesignSize: 4cm x 0.4cm/1.57" x 0.16" (Approx.)Notes:Due to the light and screen setting difference, the item& 39;s color may be slightly different from the pictures.Please allow 1-3cm dimension difference due to different manual measurement.Package Included:1 x Carbon Dioxide Check Valve