North American Aviation Part Numbering System

The North American Aviation Part Numbering System: A marvel of ingenuity during one of the most chaotic times in American history

At AirCorps Library and AirCorps Aviation we geek out and obsess about part number methodology. It helps us do our jobs better, and keep digitized part drawings organized. Some aircraft manufacturers during WWII had no apparent part numbering system, while others established complex organizational systems that unleash a wealth of knowledge simply by understanding their unique systems. At AirCorps we always say that North American Aviation "did it right". Their part numbering system was so detailed and well organized that finding a drawing you need is incredibly simple once you understand the structure.

North American Aviation scaled up production of the P-51 Mustang in under 100 days, in addition to building numerous variants of the B-25, AT-6, and T-28 during WWII. This breadth of work required an incredible amount of organization and planning to accommodate the design changes, revisions, drawing updates, and aircraft variants. Because of this, the creation of a comprehensive part numbering system, and the process for giving each part or assembly a part number had to be very intentional. In this blog I will explain the structure of the NAA part numbering system that contains every North American manufactured part utilized on all of their aircraft.

Part Numbers / Assembly Numbers / Drawing Numbers

The terms, part number, assembly number, and drawing number are essentially interchangeable, which can cause some confusion. Individual aircraft parts such as washers, springs, and sheet metal panels were all given part numbers, but so were the larger assemblies that they were a part of. The term "drawing number" comes into play because there is a drawing for each of these parts and assemblies, and the part number for them is listed on the drawing, and is how the drawing is identified.

For example, part number 102-54259 is the the spring used inside the landing gear position indicator switch protector seal used on the P-51. The spring is an individual part, so it makes sense that it has a part number. This spring fits into the larger seal assembly for the landing gear position indicator switch protector. The seal assembly is part number 102-54257, and shows the springs location within the assembly, along with the part numbers of the other individual parts that make up the seal assembly.

Assembly drawings continue to get increasingly complicated as the assemblies increase in size, but all of them still have their own individual part number. This is why there are so many drawings for an aircraft. Not only are there the thousands of drawings and part numbers depicting individual parts, but also thousands more depicting the ways that all those individual parts fit together into larger and larger assemblies!

Where to find a part number on a North American Drawing

North American part numbers are always located in the title block at the bottom right hand corner of the drawing. This was a standard placement for all part drawings amongst WWII manufacturers. The part number is also printed two additional locations of an NAA drawing, on the outside margin, and in the upper left corner of the title block. In the drawing below you can see an example of the different areas on a drawing that a part number can be found.

NAA Part Numbers - A Number in Two Parts!

North American part numbers can easily be identified because they consist of a PREFIX of 1 to 3 digits, followed by a hyphen, and a SUFFIX of 5 to 6 digits. The part number prefix identifies the model of aircraft that the part was originally designed for, whether or not that part was later used on other aircraft. Several NAA prefix examples:

For a detailed list of part number prefixes for North American, and other aircraft manufacturers, CLICK HERE.

Part Number Prefixes for the P-51 Mustang  

Since the P-51 is one of the most discussed Warbirds, I thought I should also included a detailed breakdown of the part number prefixes associated with the Mustang. There are 15 prefixes associated with the P-51, some of them more utilized than others. The cart below shows a breakdown of these 15, and which P-51 models each pertains to. This prefix information can be used in conjunction with the part number suffix chart in the "whole bag of suffixes" section below.

Suffix Details

The suffix of a NAA part number tells you specifics about the part itself. The first two digits of the suffix identify the part by determining the functional group for which it was designed, regardless of its location in the airplane or its method of attachment. For example, a part number in the -58000 series indicates a hydraulic part, while a part number in the -54000 series indicates the part is used in an electrical system. This means that no matter the prefix that is model specific, all the drawing that share a similar suffix deal with the same functional group, but can be for different aircraft. At AirCorps Library we use this part numbering system to categorize our drawings for each model of North American aircraft.

Some NAA suffixes are very specific, and always mean the same thing - such as:

-00001 = Three View Drawing

-00003 = Inboard Profile

-00002 = General Airplane Assembly

-00010 = Markings

Within this system, it's easy to see how several drawings can have an identical part number suffix, with different prefixes that indicate they are for alternative aircraft models, for example:

102-00010 = Markings drawing for P-51B and P-51C

106-00010 = Markings drawing for P-51D and P-51M

108-00010 = Markings drawing for B-25J

117-00010 = Markings drawing for P-51H

121-00010 = Markings drawing for AT-6F

159-00010 = Marking drawing for T-28A

Notice that the suffix stays the same in the markings drawings above, while the prefix indicated model applicability.

The Whole Bag of Part Number Suffixes:

Beyond the very specific suffixes listed above that start with a series of zeros, every other NAA drawing fits into a more general suffix (functional group). The chart below breaks down the suffix groups within the NAA part numbering system. This information is taken directly from North American technical manuals - they were very conscious about providing factory workers and mechanics with the information they needed to educate themselves - what an idea!

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