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What's the difference between an "inside diameter" and an "outside diameter"?
Last Updated: 02/25/2015
The inside diameter is the distance between the inside of the circular opening of the tube. The outside diameter is the distance between the outside of the tube. To find the inside diameter, when only provided with an outside diameter and wall thickness, take the outside diameter (OD) and subtract the wall thickness twice. Example: If a tube has a 3" OD and a .125" wall thickness, what is the inside diameter (ID)? 3" OD minus .125" (for the first wall), minus .125" again (for the second wall) = 2.75" ID.


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