# Quick Question:  Exhaust Nomenclature

**URL:** <https://forums.speedlife.net/t/quick-question-exhaust-nomenclature/13124>\
**Category:** NYSpeed Automotive\
**Created:** [June 9, 2006, 3:54pm UTC](https://forums.speedlife.net/t/quick-question-exhaust-nomenclature/13124 "2006-06-09T15:54:52Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Fry](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/fry/32/7284_2.png) [@Fry](https://forums.speedlife.net/u/Fry)\
**Post date:** [June 9, 2006, 3:54pm UTC](https://forums.speedlife.net/t/quick-question-exhaust-nomenclature/13124/1 "2006-06-09T15:54:52Z")

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Does an exhaust’s spec’d diameter typically refer to the OD or the ID? I’m sure there are exceptions to every rule, but in general…

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**Author:** ![Blue\_Eyed\_Devil](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/blue_eyed_devil/32/7292_2.png) [@Blue\_Eyed\_Devil](https://forums.speedlife.net/u/Blue_Eyed_Devil)\
**Post date:** [June 9, 2006, 6:28pm UTC](https://forums.speedlife.net/t/quick-question-exhaust-nomenclature/13124/2 "2006-06-09T18:28:06Z")

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The od is not really important(obviously) but, some companies list the od so it seems larger.  
I think most people assume the id is listed because it more matters.

Edit: I actually called a place and they admitted on the phone that their exhaust is not really 3". They told me it was 2.750 with a .062 wall so it was 3" od.:smash2: Nice math skills.

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**Author:** ![newman](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/newman/32/7569_2.png) [@newman](https://forums.speedlife.net/u/newman)\
**Post date:** [June 9, 2006, 6:32pm UTC](https://forums.speedlife.net/t/quick-question-exhaust-nomenclature/13124/3 "2006-06-09T18:32:49Z")

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schedule pipe is neither. But the ID is closer to the nominal size.