54221Hi, stop your steps 100% brand new and high qualityIt can prevent the aquarium water from flowing back, which is caused by the CO2 pressure drop, and maintain the function and service life of the co2 bottle. When used in an ozone generator, it can prevent ozone from entering the air pump back and erosion of the propeller. It can protect the power head from flowing water, which is caused by cutting off the power. Fits standard CO2 aquarium inner diameter (4mm). Material: Stainless Steel Size(L*W):40mm x 4mm (Approx.) Color: SilverQuantity: 1pc(Air pump is not included!)Note: Please allow 1-3mm error due to manual measurement. Pls make sure you don't mind before you bid. Due to the difference between different monitors, the picture may not reflect the actual color of the item. Thank you!