What is the difference in callout size for interchangeable IPS to CT for the same OD?

When considering the callout size difference between interchangeable Iron Pipe Size (IPS) and Copper Tube (CT) for the same outer diameter (OD), the correct answer is a difference of 1/4". This is because IPS fittings are designed to accommodate a specific taper and threading that corresponds to the nominal pipe size, which results in a larger interior diameter compared to CT fittings that rely on a different sizing standard.

In practice, for a given outer diameter, the IPS Callout will be larger than the CT Callout by a quarter of an inch. This difference is essential for ensuring proper fit and compatibility when connecting various piping systems and fittings.

Understanding this sizing difference is crucial for anyone working with plumbing or piping systems, as using incorrectly sized components can lead to leaks and inefficient system performance. The 1/4" size difference is a standard recognized in industry specifications, making it essential knowledge for professionals in the field.