A part is interchangeable with another part when (a) the relevant functional and physical properties are equivalent in performance, reliability and maintainability, and (b) can be used without requiring special procedures (such as selecting for fit or performance) and without altering the part itself or any other part. A part is often considered interchangeable with another when the form, fit and function are identical.Practically speaking, if a new part can be intermingled with previous iterations of that part without any negative effect, then it's interchangeable. The part is "revised", retains the same part number, and is received into the same inventory location. Conversely, if you need to stock a new iteration of a part in a different inventory bin because it is not compatible with previous iterations, then it's not interchangeable. You must issue a new part number.