The Edelbrock Blow-Down Tube vents nitrous oxide out of your vehicle if the safety disc breaks due to over-filling or over-heating. This blow-down tube is 22. This aluminum, black, blow-down tube has a -8 AN female thread. A blow-down tube is an essential safety feature for hatchbacks or cars with the bottle mounted in the passenger compartment. The blow-down tube will safely vent the nitrous to the outside of the car.