How are Aftermarket Parts Catalogues Different from OEM Catalogues?

January 28, 2022
How are Aftermarket Parts Catalogues Different from OEM Catalogues?

As e-commerce increasingly becomes a dominant driving force in the car part industry, more and more businesses are looking to build a functional and easy-to-use online car parts store.

However, building an online store that allows end-users to purchase car parts directly is not an easy task. Aside from building a website capable of handling inventory and making it seamless for purchasers, you will need a reliable auto part catalogue to manage all the parts effectively. 

One area of concern when building an online car parts store is the use of an aftermarket car parts catalogue. These online catalogues contain aftermarket parts, which are parts from third-party suppliers and car part manufacturers. Distinguishing the different types of auto parts and how they connect together is an important part of maintaining your catalogue for ecommerce.

Types of Auto Parts

The origin of a car part is very important to consider when building an aftermarket part catalogue. Below are some fundamental differences between these kinds of parts.

OEM parts

OEM parts, or Original Equipment Manufacturer parts, are the parts that are manufactured or used by the original manufacturers of the vehicles themselves. Because these parts are found originally fitted in your vehicle, you can expect them to be a direct replacement.  

However, these parts are generally more expensive than the other choices. They are also not very widely available, so it can be quite hard to find a reliable source for them online.

OCM parts

OCM parts, or Original Component Manufacturer parts, are close to the same as  OEM parts. They are made in the same factories as OEM parts, and they go through the same testing standards before being released into the retail market. The only thing they are missing is the same branding as OEM parts. Thus, OCM parts can perform just as well as OEM parts, allowing you to easily replace or swap out one for the other. 

OES parts

OES parts are Original Equipment Supplier parts. These are parts that are manufactured by an official third-party manufacturer and are fitted directly in the original vehicle build. Often these parts will have both the OEM part number as well as the OES part number stamped on them. At times, OES parts are simply referred to as “OE” parts.

Aftermarket parts

Aftermarket parts are markedly different from OEM parts as they are not manufactured by the original car manufacturers. These parts are often less expensive than their counterparts. There is a huge range of aftermarket part manufacturers, around 30,000 globally. Therefore, it is difficult to make any generalizations about these parts.

Aftermarket parts might not be designed by the original car manufacturers, but they are generally capable of putting out high-capacity designs that can rival the original. Therefore, once the fitment issue with aftermarket parts is resolved, customers can confidently buy them to replace the faulty parts of their car, if they can be sure the part is going to fit.

OEM vs Aftermarket Parts Catalogues

Both OEM and aftermarket parts are fundamentally different from one another. 

OEM catalogues are designed and managed independently by each OEM, or OEM group. This means that the structures are generally not compatible with each other. Vehicle structures are not defined in the same ways, parts may be called completely different names and sometimes be referred to in different languages altogether. Generally, OEM catalogs are designed based on the particular vehicle and will contain assembly-level diagrams. This is very useful when looking to replace one individual part. However, the structure and inconsistency makes it close to impossible to utilize OEM catalogues as the base for any online selling, or ecommerce. 

On the other hand, due to the large number of aftermarket manufacturers, and the wide range in size of manufacturer, there are few who design and manage their own internal parts catalogue structure. Many aftermarket manufacturers do not manufacture a large range of parts like an OEM, and therefore it would not make sense to maintain a complete parts catalogue. 

This causes aftermarket manufacturers to generally rely on third-party managed cataloging solutions. There are many ways in which these cataloging solutions can be managed. Some are based on the OEM structures, reconciling the differences into a central catalogue. Others build a new structure based on the aftermarket manufactured parts.

The backbone of any catalogue is the vehicle data. How are the vehicles structured? How is a part linked with a vehicle to mark compatibility? What level of differences between vehicles are recognised within the catalogue? These are the types of questions that need to be answered. 

When selling online, the key is to be able to manage all the data in one place. All the data means cross-reference information (links between equivalent part numbers) as well as vehicle compatibility information. As soon as this information needs to be maintained in different places with different formats, it opens a rabbit hole of issues.

How to choose the best aftermarket parts catalogue

It should become clear now that an aftermarket parts catalogue requires a lot of attention and is the basis of all auto parts ecommerce. So what matters if you want to get this right? 


Accuracy is of utmost importance when you choose an aftermarket parts catalogue. Aftermarket parts are not manufactured by original manufacturers, so the fitment data must be completely accurate to prevent misfits. Be sure to find an auto parts catalogue that consistently provides reliable fitment data.


Apart from giving out accurate fitment data, the catalogue should also be complete. It means that the catalogue should include all the possible vehicles that the parts might be compatible with. 

This will not only help customers but also can make sure that your online car parts store will not lose any potential sales. The databases GAPC and UVDB - which power Partly API and PartsPal - are some of the most comprehensive databases in the world, handling more than 70 million parts. 


It is very important to scale your business onto other e-commerce platforms. Multi-channel e-commerce businesses are becoming more and more common. If these platforms do not use a shared fitment data format, it can be extremely difficult to process the data and work with it. Consider using a car parts catalogue, like Partly, with a universal data format so that all of your platforms could use highly accurate fitment data with ease. 

Aftermarket parts catalogues are extremely important for any online car parts store that wants to be ahead of its competitors. As aftermarket parts are more difficult to manage, and their fitment data is considerably important, an accurate, functional, and well maintained car parts catalogue for these parts should be an indispensable part of your e-commerce website. 

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