id go grab a filter at autozone, advanced, wherever..then I brought my filter inside Home Depot to check what fit correctly. I had a 4 inch by 9 inch k&n, then I believe the tb and maf is 3.25. I don't remember though. But the standard 3 inch couplers from Home Depot is what I got. The thing you need to worry about is the cone. So if you get a 3 inch cone you can run 3 inch straight. Mine had the flare to fit the 4 inch.