There is a saying: “if you change form, fit or function, you change the part number.” On the surface this seems like a good saying. People use this saying as rule of thumb to determine if a new part number is required.  Taking out new part numbers cost the company some administrative time and effort (also known as “money”), and it can be good to eliminate that burden. However there is more to this than the typical form, fit or function evaluation method.

Some companies use part numbers to track the quality of the product. In fact, many or most do. They monitor the parts returned by part numbers for signs that their quality is eroding.  Not changing part numbers makes distinguishing the failure and cause or even an improvement in quality and cause difficult.  For example, perhaps we make a small change to our manufacturing process. This change has no implication on form fit or function of the product.  However, this change may have some cascading impact on the quality of the product in the field.  By not changing the part number and linking this to the process change we are unable to readily see any dependent consequence on our product in the field. If the customer or the government demands a recall, such a response becomes extremely difficult without the ability to recover the offending part numbers. In fact, if we do not have this level of traceability, we may have to recall all of the product at great expense to all involved.

A more prudent action would be to consider the cost of creating a new part against being able to more readily discern changes in the product and symptoms witnessed in the field.  If you change anything in the product or the process (including a supplier of subassemblies) consider altering the part number. Perhaps the saying should really be, form, fit, function and quality.