Description These are CO2 reactor quick twisting Bottle Caps, made of high-grade ABS material, which are safe and durable and can be used with confidence. It is suitable for all kinds of DIY reactors, and can be directly screwed to carbonated beverage bottles for use without air leakage, which can bring you a good experience.Easy to use. Just screw the bottle on the drink bottle. Easy and sealed without letting the air out easily. Features -Color:Beige-Material:ABS-Size:5.50X4.00X4.00cm/2.16X1.57X1.57in- The installation method is simple and will not take you too much time. It can help you a lot.- High class ABS for issuing great resistibility of rub, so it is durable and practical. - It has a simple design, but very practical in use, bring much convenience to you.- If it is blocked after a long time of use, it can be restored to normal by dredging the air hole with cotton swab .- CO2 System Bottle Caps are designed for low cost planted tank use. It is very useful.Packing list: 2 x Bottle Caps2 x Sealing Rings