Material numbering is the process of assigning unique identifiers to materials in the system. Material numbering is defined at the client level, which means that the same material number can be used for different materials in different clients. However, within a client, the material number must be unique for each material. The material number can be either external or internal. External material numbers are entered manually by the user, while internal material numbers are generated automatically by the system. The maximum material number length is 40 characters for external numbers and 18 characters for internal numbers. The material number length can be customized in the configuration app Define Material Number Lengths1. The material number can also be formatted with prefixes, suffixes, and templates in the configuration app Define Material Number Formats2. References: Define Material Number Lengths | SAP Help Portal, Define Material Number Formats | SAP Help Portal