21B4

21B4 is an alphanumeric designation used in various catalogs and systems to label a model, part, route, or document. It does not refer to a single, universally recognized entity; its meaning is determined by the context in which it appears.

In transportation and infrastructure, codes of this form are commonly assigned to specific items or services by operators or manufacturers. A transportation agency might designate a vehicle component, a station code, or a maintenance task with the label 21B4, with the exact reference varying by region and internal labeling conventions.

In manufacturing and electronics, 21B4 may serve as a product or part number. Companies use such codes to identify components, assemblies, or accessories within a catalog or supply chain. Without accompanying metadata (manufacturer name, series, or specification), the code is ambiguous.

In documentation and cataloging, 21B4 can function as an internal reference, version tag, or archive identifier. It may appear in technical manuals, service bulletins, or library records, again dependent on the issuing organization’s coding scheme.

Because 21B4 is not unique to one subject, readers should rely on the surrounding information—such as the company, product family, date, or system—to determine what the code refers to in a given instance. See related patterns such as 21B or B4 for examples of how alphanumeric codes are structured across domains.