In the manufacturing industry, the part number (AKA part code, item code, etc.) is a (theoretically) unique identifier attached to every "object" entering the finished product.

This apparently trivial piece of information lies at the very heart of the manufacturing process, and is essential to logistics, purchasing, stock and inventory management...

Part numbers should designate a unique combination of "Form, Fit and Function" (this is known as the three F principle): every change in one of these factors should require a different part numbers: conversely, items that are perfectly replaceable (interchangeable) should have the same part number. Failure to comply with this principle is a common source of manufacturing and/or maintenance errors.

A complimentary, common, and costly mistake is having interchangeable parts filed with different part numbers, which multiplies all the associated inventory costs.

The (often hierarchical) list of all the part numbers that are used in a product is called the Bill of Material (BOM) and constitutes the second sacred cow of manufacturing.

If you would like to be subjected to an endless droning on part numbers and BOMs, any PDM or ERP consultant/vendor will be glad to satsify your urge. If you want