XINXU Features: CO2 system is designed for low cost planted tank useEasily set up/low cost/excellent qualityThis bottle cap is very well suitable to be DIY Co2 system's accessory that the size fits common PET plastic bottle.As for the another advantage of specific, we attached the great quality plastic O ring inside of the cap to prevent missing the Co2.Easy set up, excellent design.Description:The composition is used as special high quality plastic for issuing great resistibility of rub, so it can be used for a long time.Easily set up/low cost/excellent quality.CO2 system is designed for low cost planted tank use.This bottle cap is very well suitable to be DIY Co2 system's accessory that the size fits common PET plastic bottle.Specifications:Material: ABSdiameter: The diameter of the bottle cap is about 3.4cm, the height is about 3.2cm, and the error is about 1cmPackage Content:2 pcs