Auto Industry Product Identifiers (SKUs, MPNs, GTINs, and More) – All You Need To Know

If you work in the automotive parts and acccessories industry, you’re juggling a lot of product identififcation data: SKUs, MPNs, ASINs, UPCs and GTINs, distributor part numbers, etc. It’s ridiculous.

Thes reason we have so many of these ID numbers?

1. Each manufacturer has their own part number for cataloging purposes, fitment data purposes, and of course ordering.
2. GTIN and/or UPCs are often used to track inventory, but third parties (like Amazon and Google Merchant Center) often require these numbers to upload data.
3. Warehouse distributors often have their own unique SKU which is needed for ordering.
4. Many ecommerce companies and retailers have their own internal SKU for their website or internal inventory management.
5. Amazon has their own unique SKU called an “ASIN” you that’s used for orders, reporting, advertising, inventory, etc.

Fun, right? Lots of numbers that are easy to transpose, confuse, import incorrectly, etc.

The goal of this article is to help auto parts and accesorries industry folksy understand what these different numbers are, and offer some suggestions for dealing with this mess.

Let’s Define All These Damn Numbers

Let’s start with some definitions:

SKU – Stock Keeping Unit: Typically an alphanumeric designation for a specific part that’s created by a retailer, distributor, or manufacturer’s internal use. It can be whatever the SKU “owner” wants it to be. SKUs are not consistent from one manufacturer to the next, retailer to retailer to retailer, etc., which means they can “collide” (when two or more different products have the same SKU, that is “SKU collision”).

UPC – Universal Product Code: A number that identifies a specific product, managed by a registration company called GS1 for a fee. Because UPC numbers are registered, they act as a universal ID that all retailers can use to identify products (at least in theory).

GTIN – Global Trade Identification Number: GTINs are essentially the same as UPCs, only technically a UPC is a GTIN…it’s confusing. GTINs are linked to specific individual products.

EAN – International Article Number: Europe’s version of the UPC, but also technically a GTIN.

MPN – Manufacturer Part Number: This is usually a manufacturer’s SKU – manufacturers will reference their own part number when they provide fitment data (eg a list of the vehicle makes and models a part is compatible with), catalog data (eg photos, descriptions, specs, dimensions, etc.).

ASIN – Amazon Standard Identification Number: A SKU for Amazon.com, but because Amazon tracks all their SKUs precisely, an ASIN can be a form of unique identification like a GTIN or UPC.

Brand Code – A four letter code issued by the Auto Care association that corresponds to a specific parts brand/manufacturer. You can look them up or free here, you just have to register an account. Because brand codes are always unique, they can usually be used with MPNs to create a unique SKU.

In terms of formatting:

• GTINs (which includes UPCs and EANs) are always numbers. Most of the time, a GTIN starts with several zeros.
• MPNs and SKUs can be letters or numbers, with or without dashes. SKUs and MPNs can even have spaces (only it’s really really dumb to put a space in a SKU/MPN).
• ASINs are always letters and numbers

Best Practice – Never Trust Anyone Else’s SKU (or MPN)

As mentioned above, SKUs and MPNs are a free-for-all. There’s no consistency, and there are dozens of situations where completely different manufacturers will use the exact same SKU for completely different products. This is called SKU collision, and it’s not good when it happens.

To avoid SKU collission, many distributors and retailers use their own SKU system. They often add a prefix to an MPN, as that’s a good way to make sure the SKU is unique while helping humans look at the SKU and know what it is.

For example, if all the Westin brand products that are available from a distributor have a “WESTIN” SKU prefix, it’s easy to tell when you’re looking at a Westin product.

Can’t We Just Use GTINs To Track Everything?

If you’re thinking, “Why would anyone bother to create their own unique SKU for every part when they could just use a UPC or GTIN?”, you’re definitely thinking about this problem the right way. Unfortunately:

• Not every manufacturer invests in GTINs/UPCs. GTINs/UPCs have to be registered with a company called GS1, and because GS1 charges a surprising up-front fee for registering these numbers, and another annaul fee to maintain the registration. Many manufacturers don’t bother because of the expense.
• Some UPCs are recycled. Because of the cost of registering new GTINs, some manufacturers will buy “used” UPCs that were registered decades ago by defunct retailers. These old GTINs are unique and associated with products that no longer exist (imagine a house brand from JC Penney – every product had a GTIN, but no one has used it in decades). Re-use of old GTINs is not allowed by GS1, but for a variety of reasons several manufacturers use recycled GTINs (they often don’t know they’re doing it).
• GS1 doesn’t give away GTIN data. Believe it or not, the company that has a global monopoly on product identification number registration doesn’t grant free database access to look parts up by GTIN. So, even if a manufacturer pays to register a GTIN with GS1, they can’t assume their customers will have a way to check/cross-reference the data.

GTINs are sort of a necessary evil. They’re hard to get away from because they’re so common and well-supported, but they’re also kind of a racket…GS1 charges a handsome fee to distribute GTINs and we’re not exactly sure why they charge so much or how they can get away with it.

Sidebar: If you’re a state or federal regulator, please look into GS1’s defacto monopoly.

What About Tracking Everything With ASINs?

An ASIN – or Amazon Standard Identification Number – is Amazon’s official SKU for a specific product. However, because Amazon is a behemoth, its ASINs are often used by retailers as a form of UPC. This isn’t a bad plan (ASINs have a lot of advantages in terms of tracking and lookup), but it’s not foolproof because Amazon doesn’t necessarily have ASINs for every product.

Also, Amazon sort of requires new products listed on its site to have a GTIN (there is a way to request a GTIN exemption, but it’s not well documented). As a result, if a product has an ASIN, it probably has a GTIN as well.

OK Fine – I’ll Make My Own SKUs. How Should I Do That?

Because SKUs and MPNs aren’t always unique, and GTINs or ASINs aren’t always available, your company may decide to use its own SKUs to track every product. If so, we have some suggestions:

1. Come up with rules/guidelines for creating SKUs that you and your staff can reference whenever a new part comes in.
2. Use a mix of letters and numbers.
3. Think about ways to include essential specs in your SKUs, like part brand/manufacturer, part finish, part type, item count, location in the warehouse, and so on.
4. Try to keep it short enough to remember so that you don’t have to immediately write it down when you see or hear it, assuming you’re manually picking, packing, and shipping.
5. Never start a SKU with a “0” (zero) or a letter “O”.
6. Never use a space in your SKUs.

For example, the SKU AFE-SAT-5.4-1283-E could refer to an AFE air intake with a SATin part finish that fits on a 5.4L V8 with the internal stock number of 1283 that’s stored in section “E” of the warehouse.

OR, that SKU could be simplified to AFE-SAT-1283 or just AFE-1283. Whatever makes sense to you.

Some More DIY Part SKU Examples (For Inspiration)

Example SKU: SSTAIL101524

SKU indicates product material, part type, and age:

• Material: Stainless Steel
• Part: Tailpipe
• Purchase Date: 10/15/2024

Example SKU: WPSILV60

SKU indicates part type and fitment:

• Part: Water Pump
• Fits Vehicle: Silverado
• Engine Size: 6.0L

Example SKU: ALT-GM-140-75CORE

SKU indicates part type, manufacturer, amperage, and core deposit:

• Part: Alternator
• Manufacturer: GM
• Amperage: 140
• Core Deposit: $75

Fake Example SKU: YUR2SLO

No offense!

Another Fake Example SKU: OU812

Who says this SKU business can’t be fun? Organizing an auto parts website is a hoot!

SKU Dos And Don’ts

We’re just going to keep going on and on about SKUs until you fall asleep…

SKU Dos

1. Keep it simple, so that you can train new hires to read them quickly.
2. Keep it short…but not so short that it doesn’t contain helpful info.
3. Start with letters to make sorting easier.
4. Use letters, numbers, and dashes. Special characters like _ ! @ * | don’t always play well with inventory management systems.
5. Document the SKUs somewhere important, and make that info available to everyone who works with your inventory.
6. Document the SKUs in your accounting system.

SKU Dont’s

1. Don’t re-use SKUs for different parts…if you have a SKU for a part that gets discontinued, that SKU should be discontinued as well.
2. Don’t use the letter “O”, the letter “i”, the letter “L”, or any other characters that can be easily confused.
3. Don’t use non-standard characters, like &, ~, ^, $, |, etc. The problem with these characters is that they’re not always easy to say or type into a computer. And, some data systems don’t support them.
4. Don’t use a SKU that’s so detailed it becomes unwieldy.
5. Don’t let anyone change your SKU system without good cause. Once you set up a SKU system, changing it can be a lot of work, and it can make historical analysis/records look-up that much harder.
6. NEVER start SKUs with the number zero. The first time you import data into Excel, there’s a good chance those zeros disappear.

In Summary

Ideally, all auto parts and accessories companies would be following one universal part numbering system that corresponded to a recognized fitment code, but that’s just not the world we live in.

So, if you’re a retailer trying to deal with all this data, you want to:

• Develop your own SKU system that makes finding parts and fulfilling orders easy.
• Keep track of MPNs, alternative SKUs, ASINs, and GTINs (which includes EANs and UPCs) for every SKU, as they can be really helpful for ordering, cross-checking, and more.

We often tell our clients that parts ecommerce is a data business, and SKUs are just one aspect of this data. Accounting for product catalog data like SKU, MPN, GTIN, and UPC doesn’t scratch the surface when it comes to fitment, cross-reference, dimensions, variants, and so on, but we’ll leave that for another post.

Have fun!

Updated May 2025.