When it comes to aviation and aerospace parts, one small detail can make the difference between ordering the right component or ending up with something that doesn’t fit your aircraft’s requirements. Two of the most common sources of confusion are Cancelled NSNs (National Stock Numbers) and Alternate Part Numbers (P/Ns).

This post will break down what they mean, why they exist, and how you can use that knowledge to avoid costly mistakes.

What is an NSN?

An NSN (National Stock Number) is a 13-digit identifier used by the U.S. Department of Defense and NATO allies to standardize parts across military and government supply chains.

Example: 5305-00-123-4567
The NSN ensures that the part meets specific specifications, dimensions, and performance requirements, regardless of the manufacturer.

Think of it as the government’s “catalog number” for a part.

What Does a Cancelled NSN Mean?

Sometimes an NSN is marked as “Cancelled.” This means it has been officially withdrawn from the supply system. Reasons include:

The part is no longer in production.
It’s been replaced by a newer NSN.
The item became obsolete or consolidated under another listing.

Important: A cancelled NSN doesn’t necessarily mean the part is unusable. Surplus stock may still exist, and some repair manuals continue to list the old NSN for years.

What Are Alternate Part Numbers (P/Ns)?

Unlike NSNs, which are assigned by the government, part numbers (P/Ns) are created by manufacturers. Over time, a single part may carry multiple P/Ns due to:

Manufacturer updates or mergers
Design improvements
Packaging differences
Licensing or supplier changes

This creates “Alternate P/Ns” — different numbers that may reference the same functional part.

NSN vs. Manufacturer Part Number – Why the Difference Matters

Here’s where it gets tricky:

The NSN guarantees certain specifications (dimensions, tolerance, performance).
The manufacturer’s P/N may vary slightly in attributes like material finish, coating, or other features that are not always critical but can matter depending on the application.

For example, an NSN might require a bolt to meet a tensile strength rating, but two different manufacturers could supply the part in different coatings (cadmium-plated vs. stainless). Both are acceptable under the NSN — but not always interchangeable depending on your aircraft system and environment.

How to Check for Replacement NSNs

When an NSN is cancelled, it doesn’t always mean the part is obsolete. In many cases, a replacement NSN is issued to reflect an updated specification or cataloging change. These replacement numbers can be verified in official resources such as the WebFLIS database (Federal Logistics Information System), through NATO databases, or in updated repair manuals.

Why This Matters to You

Cancelled NSNs: If your manual lists one, it may now point to a replacement NSN or alternate P/N. Without knowing this, you might think the part is unavailable when it’s not.
Alternate P/Ns: If you order strictly by a manufacturer P/N without checking NSN equivalency, you risk buying something that looks similar but doesn’t meet the required spec.

Final Takeaway

Cancelled NSNs and Alternate P/Ns are common in aviation parts — but they don’t have to be confusing. Understanding the difference ensures you:

Avoid ordering mistakes
Maintain compliance with required specs
Save time and money on reorders

If you’re ever unsure about a part number, reach out to us. We’re here to help you make the right choice.