National Stock Numbers (NSNs) are used to provide standardized identification for aerospace and defense parts, creating a foundation of traceability and uniformity across international supply chains. Because sourcing these highly regulated components often involves complex challenges like shortages, obsolescence, or urgent repair needs, substitution is often necessary. In this blog, we will examine when part substitution is appropriate, how specialists validate alternatives, and what risks should be managed throughout the process, so read on to learn more.