What is an OEM part number, where is it written, and how do you find a part by it?

An OEM part number is the number the vehicle or machine maker gives a part in its own parts catalogue; catalogue data calls it the OE number. It sits on the part, on a nameplate or marked into the body; failing that, the maker’s catalogue gives it through the chassis number. Independent catalogues link their products to OE numbers, so it is also the key to a compatible part.

What is an OEM part number?

An OEM part number is the number a vehicle or machine maker assigns to a part in its own parts catalogue. OEM stands for original equipment manufacturer, and catalogues shorten the same thing to OE number. TecAlliance, which publishes the TecDoc catalogue, describes its OE data as “sourced from official Electronic Parts Catalogues (EPCs)”, the vehicle makers’ own catalogues.

The word is not used the same way everywhere: Volkswagen’s classic parts shop uses OEM for the suppliers of the original equipment.

Where is the OEM number written on the part?

The number is stamped or engraved into the body of the part, or carried on a nameplate, and the place depends on the type of part. Three manufacturers describe their own practice:

• Turbocharger: Garrett turbos carry their numbers on a nameplate on the turbo housing. OE nameplates “can be engraved or plated on the turbo housing”, and the details vary with region and assembly plant.
• Piston: IPD, an engine parts manufacturer, says in a bulletin on Caterpillar pistons that the part number is read from the crown, where it is “usually stamped, etched, or inked”.
• Volkswagen parts: Volkswagen Classic Parts gives the identification features of an original part as “the embossed VW logo, the part number or, of course, the nostalgic original packaging”.

A pipe with no readable number is described by its measurements, as covered in a separate article.

Is every number on a part the OEM number?

No. A part carries other numbers as well: a casting number, and the supplier’s own part number. A casting number belongs to the rough, unmachined part. IPD’s bulletin makes the point with pistons:

“Identification or casting numbers in the skirt or body of the piston may not represent the actual part number of the finished piston.”

IPD, Technical Bulletin IPDTB-0004, August 2021

In the bulletin’s example, a rough piston marked 1073565 on the skirt is machined into either part 1073565, with one valve relief, or part 1654262, with two. The maker can “machine these rough forms into several different finished piston part numbers”, so the casting number does not tell those two apart.

The second number is the supplier’s. On the nameplates of turbos Garrett supplies to vehicle makers, two numbers can appear: the “Customer or OE part number” and the Garrett part number. Garrett’s own number also changes with the sales channel; its heading for this is “Same turbo – different sales channel”.

Source: Garrett, Turbo Identification page. The numbers and channel names are Garrett’s; none of them is the vehicle maker’s number. Garrett uses OES for a turbo sold through the vehicle maker’s spare parts network, in that maker’s box.

How do you find the OEM number if it is not on the part?

A number that cannot be read off the part is found in the maker’s parts catalogue, using the chassis number (VIN). The Volkswagen Classic Parts help pages say vehicles built from 1998 onwards can be searched by chassis number, giving “search results that are precisely tailored to your vehicle”. TecAlliance likewise lists the VIN among the ways to search TecDoc.

Engine parts also need the identity of the engine. IPD’s bulletin asks for “specific serial and arrangement numbers” to match a product to an engine; where those are on a Caterpillar is in a separate article. Volkswagen says its engine code “is usually located on the cylinder block together with the engine number”.

What does it mean when a part number is superseded?

It means the maker has replaced that number with a newer one, and its records tie the old number to the new. The help manual of Volvo’s dealer system defines the word:

“Supersession is the term given to the replacement of one part number by a newer number.”

Volvo, GDS Fusion dealer system online manual, Supersessions

The change is not always one for one. The manual lists three types: “Single - one part number superseding”, “Multiple - more than one part number superseding” and “Variable - i.e. for more than one model of truck”.

When a superseded number is added to an order, the system displays the replacement details; if the old part is still in stock, it gives “the option of selling these first”. TecDoc’s search types include both a “Replacement Number” and a “Replaced Number”.

OE number or article number: how do you find a compatible part?

In an independent parts catalogue you search with the OE number, and what comes back is the parts maker’s own article number. TecAlliance says the product data in TecDoc is “provided directly by parts manufacturers”; OE numbers are matched to those products and to vehicles. The TecDoc web service definition lists the search types one by one: “0: Article Number (DEFAULT), 1: OE Number, 2: Trade Number, 3: Comparable Number”.

A match is not always one for one. The same definition has a field that “qualifies how the part is interchangeable”. Its example values:

• “Interchangeable”;
• “Interchangeable, but different scope of supply”;
• “Not directly interchangeable because it is part of a kit”, or because “it’s a kit for the part”;
• “Conditionally interchangeable, may require adjustments”;
• “Supply contains more parts than the OE set”, or fewer.

Even when the number matches, check what the product covers: a single part or a kit.

What should you do before you search or order?

The order we suggest:

1. Read the number off the part. Copy every number on the nameplate and the body, character by character, and note where each one was.
2. Sort them. Do not pass a casting number off as the OEM number. Give a supplier’s number as what it is.
3. Enter it complete. In the TecDoc definition the default for a number search is “exact: Exact Match (DEFAULT)”. Garrett says of its own catalogue search: “The system will recognize the number with or without the dash.” Caterpillar’s dash and leading zero are covered in a separate article.
4. Add the chassis number. When the number is unreadable or in doubt, the maker’s catalogue is opened with it.
5. Ask whether the number has been superseded. If it has, give the old number and the new one together.

Keep the old part’s box and invoice too; they are the first place to look when the part itself cannot be read. That advice is ours; our sources do not say it.