7" ID to 6" ID - Cobra Head Reducing - RubberThis reducing cobra head elbow is 7" ID on the short end and 6" ID on the long end, and has a 1 8'NPT female pipe thread on one side. Cobra head elbows are used when clearance is extremely limited, such as when an air cleaner outlet is up against a firewall. There is no other way to make a really tight bend without losing air flow. How does the cobra head make such a tight bend without increasing turbulence? Because it flares out, creating more volume