A master alloy is formulated specifically as an additive to be diluted into a larger copper melt; its alloying element concentration is intentionally high — far above the level found in a finished alloy. An unwrought copper alloy under heading 7403 is already at its final composition and is ready for fabrication into wrought products. The intended use as a dilution additive, supported by technical data sheets or producer documentation, is the key classification evidence.

Common alloying elements include chromium, beryllium, phosphorus, manganese, silicon, and zirconium. The specific element does not change the heading — all copper master alloys classify under heading 7405 regardless of which element is concentrated. However, certain elements (notably beryllium) trigger additional health and safety documentation requirements at entry due to their toxicity.