Threaded end fits our 2-1/2'' Clear Hose (#22784, sold separately), while the opposite end is flared for easy connection to standard 4'' tool ports.
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This threaded Quick Coupler has one 2-1/2'' end with threads that fit our Clear Hose (#22784, sold separately). The opposite end is flared for quick connection to standard 4'' tool ports. Right-hand threaded.
WARNING: Cancer & Reproductive Harm - www.P65Warnings.ca.govWARNING: Drilling, sawing, sanding or machining wood products can expose you to wood dust, a substance known to the State of California to cause cancer. Avoid inhaling wood dust or use a dust mask or other safeguards for personal protection. For more information go to www.P65Warnings.ca.gov/wood. 
It was the exact size I needed. I ordered similar items the didn't even measure close to 4 inches in outer diameter!
My planer has a 4 inch dust port, but I have 2 1/2ā hose
Needed a reduction from 4 inch o.d. clear pvc to a 2 1/2 inch hose.
Because it will (I hope) do what it is supposed to
I have anew drum sander with a 4ā port. My Shopsmith dust collector has a 2 1/2ā hose