The OE code (Original Equipment Number) refers to the unique number assigned by the automobile manufacturer to its original parts. Every part used in the production and assembly of a vehicle will have such a number, which is compiled by the original equipment manufacturer (OEM) according to its parts catalog system. The OE code is often composed of a string of numbers or letters, and the length and rules vary from manufacturer to manufacturer. For example, Toyota's part number is usually in the format of "5 digits-5 digits" (such as 90915-YYYXX represents a certain model of oil filter), and Volkswagen (VAG Group) part numbers contain at least 9 characters and are logically divided into several groups, of which the first 3 digits usually represent the applicable model or engine.

For manufacturers, mastering the OE code is very important: there may be multiple supplier alternatives for a part of the same car, but they all correspond to the same original OE number. Buyers often directly ask or search for the OE code to confirm whether the accessories are compatible.