Deciphering aircraft part numbers (and inspection stamps).

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MiTasol

1st Lieutenant
6,309
10,673
Sep 19, 2012
Aw flaming stralia
This thread was inspired by a member who, incorrectly, stated that identifying part numbers was Dead easy for Spitfires as the Part number starts "300". Obviously this person got this information from someone who has never had the misfortune to work on a Spitfire so must be forgiven.

Over the years there have been a number of posts covering part numbers and serial numbers - many correct and even more which were incorrect.

I hope that those with knowledge of the thousands of aircraft types that I have never worked on will add their knowledge to this thread or expand/correct what I have written. Engine P/N deciphering needs adding - all I can say is Bristol engine part numbers start FB.

This post will set out to describe in brief detail the part number systems used by Avro, Bell, Bristol, Consolidated, Curtiss, deHavilland, Douglas, North American, Republic, Stearman, Supermarine and Vultee. You will note that I did not include Boeing because it appears that their part numbering was done by a very drunk person who had the DTs. Boeing numbers include all the systems below on the same aircraft, and even on the same major assembly - and a couple unique to Boeing.

Knowing a part number on its own is no guarantee that it comes from just one manufacturer. Bell, Curtiss, North American and Stearman all had a model 75 so all have part numbers starting 75-. Add to that the Boeing B-17 has a raft of 75- part numbers in keeping with Boeing's system of not having a system

First we need to understand the difference between Part numbers, Assembly numbers and Serial numbers.
  • Every part has a part number. This is usually the drawing number but some drawings cover multiple parts such as left and right hand versions of the same part or various lengths of the same part. In that case the drawing will have a note or table covering the differences.
  • An assembly is a collection of parts of various numbers joined together in an assembly for ease of maintenance and repair. Sometimes all the parts of an assembly have different part numbers but more often the assembly will contain multiples of some parts. Many Assemblies have Serial numbers. Think of a seat. You obviously don't want it riveted to the main structure as you have to remove it for routine maintenance so it is made as an assembly. If you are a mechanic in the middle of the Battle of Britain you do not want to change that hard to replace casting in the middle that needs a jig to accurately position it. What you want is to requisition a complete seat so the pilot can go do his job today, not next week. Likewise with airline and other aircraft today.
  • Serial numbers are used mainly on assemblies but also on some individual components. Serial numbers are only used for certain purposes:
Any part that has a "life" must have a serial number and a logbook or history card. That life can be hours or cycles before overhaul, hours or cycles before replacement (scrapping), calendar time in service and a number of other less common factors.

Any part that is part of a matched set of parts where this wing only fits this fuselage or similar​
  • Think of a seat. It is made as an assembly but usually it does not have a serial number because it is a repairable item that is completely interchangeable and has no life limitations or overhaul period. Doors and many other parts also do not normally have serials.

Next - to address the Spitfire issue that inspired this post

Every new part fitted to the Mk I Spitfire had the 300 prefix but each subsequent model has its own prefix,

If part 300nn-nnn is modified, or additional, and introduced on the Mk II it will have a 329nn-nnn part number but all the parts carried over from the Mk I will still have 300 numbers. New parts introduced on the Mk V are prefixed 349, Mk VII new parts are prefixed 359 etc. New parts for the universal wing have a separate prefix as do Vokes filter, floats, drop tanks and numerous other parts. Therefore a Mk IX for example can have an assortment of parts with all those, and other, prefixes. Every model and submodel introduces new part numbers

Some common prefixes on early Spitfires are
  • Type 329 - Mk II
  • Type 330 - a modification to the tail skid
  • Type 331 - universal wing
  • Type 337 - Mk IV
  • Type 340 - Seafire Mk I
  • Type 343 - Aux fuel tanks
  • Type 346 - a wing modification
  • Type 352 - Mk V Vokes filter
  • Type 353 - PR modifications
  • Type 355 - Mk V on floats
Note those numbers may not all be correct. My memory is not perfect by a long shot

Add to that, just to keep you on your toes, parts carried over from earlier aircraft will still have the part prefix relevant to that earlier aircraft. And yes the Spitfire does have such parts

While to some extent this appears difficult it is in fact a variation on a very common very simple theme.

Variations of the same basic concept were used by Bell, Curtiss, North American, Stearman, Supermarine and Vultee though Supermarine were the only people to have massive assemblies as the core number.

Continuing with Supermarine as an example you will get a part number like shown below - part number 30027-2517.

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Breaking this down the part number consists of three segments
  • 300 = Supermarine Type 300 being the first model this part was used on.
  • 27 = Major assembly number - fuselage complete
  • 2517 = that individual part.
  • G = the drawing issue (revision) letter which is not usually included in the part number in the part itself or in the parts list/catalog
    • If it is included then there will be restrictions on replacing with earlier or later revision parts and this will be identified on the drawing and in the parts list. Most manufacturers just give the non-interchangeable part a new number to avoid any confusion.

On Bell, Curtiss, North American, Stearman and Vultee the model number of the first type the part was used on is separated from the system number, rather than being attached to the major assembly number. With all these manufacturers the digits before the first dash indicate the model that the item was first used on.


North American - I will do this first as it is the easiest.

The five digits after the first dash indicate the individual part number with the first two digits indicating the system or section. On NAA aircraft those first two digits indicate as follows. the rest of the number is the individual part. This sort of chart is in the front of all NAA parts catalogs - this is AT-6 chart. The P-51 chart is a little simpler with no second crew member

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For the B-25 the chart is essentially the same - just additions to cover the extra crew requirements and 34001 becomes the nose landing gear. I do not have a copy of the B-25 parts catalog so cannot present the equivalent page but will find a copy. Turrets were not made by NAA so the blueprints only cover the NAA made parts necessary for the installation in the 60000 group and flexible guns are 62000.

I will detail the Bell, Curtiss and Stearman systems more in a separate post on this thread.


Avro, Consolidated, deHavilland and Republic (Seversky) used a different variation on this theme with the model number followed by one or more letters representing the assembly or system.

I will detail these a little more in a separate post.


Douglas used the simplest system and there is no way to tell from the part number what aircraft a part belongs to. The first digit is the drawing size, the remainder of the number is numerical in order of being issued. Douglas had many types in production and on post production support in the early 1940s - probably about a dozen major models without counting the derivatives. so part x may be from the SBD but part x+1 could be from DC-3 or any of its twenty odd military derivatives, DC-2, DC-4, DC-5, A-20, A-26, B-18, B-23, C-33, C-68, etc, etc, etc.

Beech numbers I never managed to decipher but I only worked on a couple of B-18/C-45 aircraft for a short time.
 
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Boeing's drawing system seems to be similar to Douglas'.

The following information is taken from Boeing document D-2706, "Drafting Room Manual", revision 44, dated 14 January 1944.

Drawing Prefix...........Size
.....1-......................8.5" x 11" **
.....2-......................11" x 17" 11" x 25.50" 11" x 34" 11" x 42.50" 11" x 51"
.....3-......................11" x 17"
.....4-......................11" x 25.5"
.....6-......................17" x 22"
.....7-......................17" x 33"
.....8-......................17" x 44" **
.....9-......................22" x 34"
...12-......................30" x 38.50" 30" x 49.50" 30" x 60"
...14-......................25.5" x 44" **
...15-......................34" x 44" **

** Width can be increased in 11" increments.

[sorry about the periods. I tried blanks, but Preview removed them, and I can't see any tabs]

The longest drawing I've seen was for a B-29 Wing Spar (8-1404, sheet 1) and looks to be around 200" long (from the chopped up microfilm version). This first sheet of 5 lists all the parts that go into the drawing. The rest of the drawings in the set range between 70"-100".

Since the B-17 and the B-29 use the same drawing prefixes, I'm guessing that the B-29 drawing numbers were picked to be different from the B-17 drawing numbers. Probably by some drawing control group that assigned the actual numbers. There might be some common drawings, but I'm doubtful.
 
Thanks for that

EAIAnalog EAIAnalog


I am sure many here would love to see a copy or a link posted on the forum for Boeing document D-2706, "Drafting Room Manual", revision 44, dated 14 January 1944.

Here are examples from the IPC for the B-17 wing. From your quotes above it would appear they had at least 94 different sheet sizes and that some higher numbers are for relatively small drawing sheets as those 21- prefix brackets are relatively small items.

Note that the only way I know of producing a tabbed table for this forum (and many others) is to do the table in your preferred word processor and then produce a screen shot of it to post to the site. Others smarter than me will know of easier ways that they hopefully will share.

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Continuing with the NAA drawings - here are the prefix tables from the B-25 (top) and F-86.

You will note that, like the AT-6 the prefixes for things like floats and flexible guns and torpedos remain in the F-86 drawing code page. Even the codes for biplanes remain in the far right column. Other codes were added as needed but none deleted. My apologies for the poor quality but these photcopies were all a friend in Brisbane had.

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Inspection stamps are another assistance as they can identify the factory an aircraft or part was built at. Great with aircraft built in more than one factory like the B-17, B-25, P-40, Spitfire etc and for identifying companies that built components like engines, landing gears, turrets, wheels and brakes, etc.

Below are several clippings from two sites that are a good start but do contain errors. On the first clipping I have marked the errors with a red outline and commented on them below the graphic. I do not know where I found this graphic. If someone knows I would appreciate a link so that I can credit the site.
1693464277867.png


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FB#### etc numbers are PART numbers of Bristol engine components. I do not remember the Bristol Filton inspection stamps.

Curtiss. The stamp shown is a Heat Treatment stamp used by many companies. The company had multiple stamps for their two factories in Buffalo New York. CWB indicates the original Curtiss factory and CWK for the second factory in Kenmore, a Buffalo suburb.

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1693464847756.png
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There are another five pages of Curtiss stamps but they are mainly less common ones you are unlikely to find. The Curtiss book also includes the following AAF stamps that can be found on any USAAF or US Navy aircraft. On older aircraft the AN will be replaced by the AC, meaning Air Corps, stamps shown on the bottom of the page.
1693465091390.png


Lockheed - that is the Vega stamp as correctly shown to the right of it. I do not have an example of a Lockheed stamp but it was an L with a long lower leg and a # on top of the leg if my memory is correct. I am sure there is a member working on a Lockheed built (as opposed to Vega built) aircraft out there who can correct me if my memory is not correct.

Supermarine - that may be one of the many Supermarine stamps or it maybe from one of the many subcontractors. I will add the Supermarine ones I know of when I find that file (if I have not deleted it by accident). There were probably over 100 subcontractors - five in the city of Trowbridge alone. There are a number of Supermarine experts on this forum who will hopefully list those stamps they are aware of.

The next post will be stamps on the site Inspection Stamps.
 
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Inspection Stamps has a page on stamps which is continuously being updated but contains many errors.

None the less it is a guide to what the stamp means though they confuse vendors and sub contractors with the airframe manufacturers far too often. Some of the stamps I do not recognise (there were hundreds of subcontractors used by US manufacturers during WW2 and subsequent) yet some are even identified as parts from vendors such as ALCOA or Bendix, etc but are treated as exclusive to the airframe manufacturer.

They have at last corrected the HT stamp error and now say



"HT" stamp note

Many planes share identical or similar heat treatment "HT" stamps. The common form is the letters HT above or below the inspector's number, all within a circle. Because of the similarity across different manufacturers' planes the common "HT" stamp is not useful in making a specific identification,
but still show many HT stamps as being specific to a particular aircraft.
Errors include identifying CCF stamps
1693466272853.png
as Beechcraft instead of Canadian Car and Foundry who were subcontractors,
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stamps as Bell instead of the subcontactors (F being Fairchild),
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as a Boeing stamp instead of USAAF/USAF,
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as Chance Vought instead of Brewster,
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as Chance Vought instead of the Vought-Sikorsky, etc.

A subsite from the same people Aircraft Prefixes by Aircraft Type contains part numbers and assigns them to aircraft models but fails to mention that, using NAA as an example, 16- numbers are common on the BT-9/10/14, BC-1, AT-6, B-25, P-51 with even a few on the P-82 aircraft. And most of their Navy variants where applicable. Naturally they leave out all the 75- numbers used on the P-40, etc, and totally ignore vendor part numbers.

That site also provides a guide to part numbers for the various types I have never worked on so I recommend it to cover my lack of knowledge in those many cases.

My next post, when I get the energy, will be Consolidated and Republic part numbers. Both being similar in that they use model number followed by letters for the major assembly followed by numbers for the individual part.
 
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Very interesting. Neither the inspections stamps or the part numbers ring any bells for me. The part number structure looks like North American but the prefix numbers are far too low and the company indicator GAAC or GACA also does not ring any bells either.

I will have to see what I can find.
 
Very interesting. Neither the inspections stamps or the part numbers ring any bells for me. The part number structure looks like North American but the prefix numbers are far too low and the company indicator GAAC or GACA also does not ring any bells either.

I will have to see what I can find.
Goodyear Aircraft Corporation?
 

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