| Compare: outer diameter
The dimension corresponding to the largest diameter measurement possible of an internal feature or cavity of a part. Generally used with respect to piping, in which it is the diamter of the tube as witnessed by the fluid inside the pipe. This can be quite a bit different than the outer diameter, for thick pipes. This is important to keep in mind when designing or purchasing reducers/enlargers to change one size of pipe to another. Also, in the US, piping is usually sold by its O.D. measurement, +/- an arbitrary amount.
|<--------- O.D. --------->|
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| |<------ I.D. ------>| |
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| | +22222222222 | |
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