This is an aluminum alloy fire hose nozzle, typically designed for 50mm (2-inch) or 65mm (2.5-inch) hoses.
It features a quick-connect type interface, often called a KDK or storz connector, allowing for rapid attachment to fire belts.
The nozzle is adjustable, allowing the operator to switch between straight-stream and fog spray patterns for fire suppression.
These are commonly constructed to be corrosion-resistant and durable for use in industrial or municipal firefighting applications.