that's wonderful, those two measurements are the two most probable sizes that the pipes are.... anyway
Mark> I loved your response, you crazy kid...
Jon> I use walker alot too, but they only list part numbers for expensive OEM exhaust parts. They make good stuff but lots of $$$... Become more resourceful, ebay, google, other places are great for listing dimensions.
Now to aid "firstwindstar02" It all depends on where along the exhaust system you need parts. Measuring the exhaust yourself is obviously the best way to do it. (Thanks GreybeardAv) The exhaust system might change pipe diameter in different locations. I know most auto stores carry these big books that hold information about cars, you can have one of those guys look up the pipe sizes.
If you are in fact talking about the flexible piece the pipe diameter is 2.5", but down near the tailpipe is 2.25" or maybe even 1.5". My advice to you is to get your butt out your chair and get under your van and measure, and if you complain about the rather rude responses you've been getting I have one thing to say, next time ask nicely.

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1998 Ford Windstar GL 3.8L 253,100 miles
2005 Toyota Prius Package 6 1.5L 135,000 miles
2006 Toyota Sienna LE 3.3L 36,000 miles
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