What an MPN is
MPN stands for Manufacturer Part Number. It is the reference the company that made the product gives it in its own catalogue — the code printed on a spare part, quoted in a technical datasheet, or listed beside a model name in a trade price list. Unlike a barcode number it is not issued by a central registry, so its format is whatever the manufacturer chose: letters, digits, hyphens, or some mixture.
Because it is only unique inside one manufacturer’s range, an MPN means nothing on its own. It works in pairs. Google reads the brand attribute and the MPN together, and that combination is what points at a specific item. Send a part number with no brand, or with the wrong brand, and the pair identifies nothing.
Why MPNs matter
Many products never receive a retail barcode. Spare parts, industrial fittings, components sold loose, and made-to-order variants all fall outside the packaged-goods system, yet buyers still search for them by their exact code. The MPN is how those items get identified, matched to the same product sold elsewhere, and shown to somebody typing a model number into the search box.
That last point is worth dwelling on. Searches containing a part number are among the clearest buying signals there are: the shopper has already decided what they want and is looking for a supplier. Carrying the MPN in your feed, and ideally in the product title and on the page, is how you become one of the results.
Where MPNs go wrong
The most frequent error is treating your own stock code as an MPN. A SKU belongs to your business; an MPN belongs to the manufacturer, and any other shop selling that item quotes the same value. Filling the field with an internal reference gives Google a code that matches nothing.
Next comes using the MPN as a substitute when a barcode exists. Where a product has a GTIN, that is the stronger identifier and Google expects it; the part number sits alongside rather than replacing it. Then there is inconsistent formatting. Manufacturers write part numbers with and without hyphens, in upper and lower case, and suppliers pass them on differently, so the same physical item ends up under several spellings. Finally, resellers often paste a whole range’s shared code onto every variant, which makes several different products look identical.
How to get it right
Take part numbers from the manufacturer’s own documentation rather than from a distributor’s spreadsheet, and record them exactly as written, keeping any leading zeros as text. Store the value in a dedicated field in your shop so it can flow into the feed, the product page and your internal search at once.
Make sure the brand attribute beside it is the manufacturer, not your shop name, since the pair is judged together. If a product genuinely has no barcode and no part number, declare that rather than filling either field with something invented, and check the Merchant Center diagnostics after each fetch to see which items are still flagged as unidentified.