AN vs MS vs NAS Hardware: What the Prefix Tells a Buyer
Buy AN or MS hardware when the drawing or parts list calls it out, since those numbers still identify the part even after the documents moved to NASM. Choose NAS or NASM documents for new design. NAS numbers come from the Aerospace Industries Association and usually encode more detail, so never swap prefixes without engineering approval.
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AN vs MS vs NAS hardware, side by side
The prefix tells you who wrote the standard and where to look up its current status. It does not, by itself, tell you whether two parts are interchangeable.
| Attribute | AN | MS | NAS | NASM and NAM |
|---|---|---|---|---|
| Name | Army-Navy standard | Military Standard | National Aerospace Standard | NAS documents converted from MS or AN |
| Origin | Early 1940s, to standardize military items for World War II | Around the 1950s, replacing most of the AN series | 1941, industry developed | Conversion of military documents in coordination with DoD |
| Who maintains it now | Mostly canceled; survivors often moved to NASM | DoD where still active; many moved to NASM | Aerospace Industries Association (AIA) | AIA, with NASM for inch and NAM for metric |
| Where to check status | ASSIST, the DoD's official source, or the superseding document | ASSIST | AIA catalog | AIA catalog, with the cancellation notice in ASSIST |
| Part number on the label | AN number | MS number | NAS number | Usually the old MS or AN number |
| Use in new design | Check status; many are canceled or inactive for new design | Check status | Active NAS documents are intended for current use | Current documents |
Origins and dates for AN, MS and NAS come from a published aircraft builder's hardware guide and AIA's own statement that NAS standards date from 1941. AIA states it maintains more than 1,100 active NAS standards, is accredited by ANSI as a standards developer, and has converted more than 500 military specifications to NAS documents carrying NASM or NAM prefixes, with parts still procured by their MS part number.
Who owns each standard
AN and MS documents are government standards, NAS documents are industry standards, and NASM documents are government standards that industry took over. Ownership decides where you buy the document and who can change it.
AN
The AN series came out of joint Army and Navy standardization in the early 1940s. Most AN documents were canceled in the 1950s as MS standards replaced them, but a few lasted for decades. The AN3 through AN20 bolts are the best known survivors, and even those were canceled by Notice 1 dated 1 December 1999 and superseded by NASM3 through NASM20 with identical part numbers.
MS
MS standards are DoD standardization documents. Their status, revisions, notices and cancellations are recorded in ASSIST, which DLA describes as the official source for specifications and standards used by the Department of Defense. The public ASSIST Quick Search site is free for most unclassified documents, and DLA states updates are processed nightly. When an MS sheet is converted, the cancellation notice in ASSIST names the replacement, for example MS21044H (21 September 1993) canceled and superseded by NASM21044, and MS20470H (14 September 1993) superseded by NASM20470.
NAS and NASM
NAS documents are written and sold by AIA as voluntary industry standards; AIA sells documents but does not supply parts. NASM documents are the former MS documents AIA adopted, and the part number usually does not change: the builder's guide gives MS20426 rivets as an example, now controlled by NASM20426 while still marked MS20426.
SAE AS
Some MS documents went to SAE International instead, and there the part number can change. The same guide cites MS21919 clamps becoming AS21919. If a drawing cites an MS clamp and the distributor offers an AS number, that is usually the same lineage, but confirm it against the SAE document.
Have a part like this?Send it in under a minute. A person replies within 1 business day.How the part numbers encode material, finish, diameter and grip
AN and MS numbers tend to use a short basic number plus dash codes and a letter or two. NAS numbers often pack more fields into the code. Read each with the standard in hand, because the same letter can mean different things in different families.
| Example | Family | How it reads |
|---|---|---|
| AN3-5A | AN bolt | AN3 is the No. 10 diameter code; no material letter means cadmium plated alloy steel (C would mean corrosion resistant steel, DD aluminum alloy); -5 is the length code; A means undrilled shank |
| NAS6203-26 | NAS close tolerance bolt | 03 is diameter in sixteenths of an inch; -26 is grip in sixteenths; an X or Y suffix marks an oversize shank |
| AN960C10 | AN washer | C is corrosion resistant steel; 10 is the size code for a No. 10 bolt |
| NAS1149C0363R | NAS washer listed as the alternate for AN960C10 | C tracks material, 03 the bolt size in sixteenths, 63 the thickness in thousandths, and the final letter the finish |
| MS21047L3 | MS anchor nut | L is dry film lubricated; 3 is the thread code, here 10-32 |
The pattern buyers notice is that the NAS1149 number carries thickness and finish that the AN960 number left to the dash and letter conventions. That is useful for receiving inspection, because more of the requirement is visible on the label, and it is also why a single AN960 entry can map to several NAS1149 numbers. The full decodes, with sources, are on our bolts and screws, washers and nuts pages.
Verified cross references and supersessions
Use a supersession only when a public record confirms it, and treat it as a document change, not proof of interchangeability. The pairs below are confirmed in the sources cited.
| Older number | Newer number or document | What the record says |
|---|---|---|
| AN3 thru AN20 bolts | NASM3 thru NASM20 | Canceled by Notice 1, 1 December 1999; identical part numbers |
| AN365 self-locking nut | MS20365, then MS21042 | EverySpec lists MS20365C (5 September 1958, 250 °F) as superseding AN365 and superseded by MS21042 |
| MS21044 | NASM21044 | MS21044H canceled and superseded by NASM21044 |
| MS20470 rivets | NASM20470 | MS20470H canceled and superseded by NASM20470 |
| MS20426 rivets | NASM20426 | Part number stays MS20426 |
| MS35338 lock washers | NASM35338 | Same part numbers |
| AN960C10 flat washer | NAS1149C0363R | Listed by distributors as the alternate, not a certified equivalent |
The AN365 row is the warning. The formal document trail runs AN365 to MS20365 to MS21042, yet the builder's guide reports a distributor that lists AN365 and ships parts labeled MS21044, and other distributor data cross references AN365 numbers to MS21044. Both may be what a given aircraft's approved data allows, but they are different standards with different documents behind them. Which one is acceptable for your assembly is an engineering and configuration control decision, and the answer belongs on the drawing or an approved alternates list, not in a purchasing system's cross reference table.
Superseded, canceled and inactive for new design
These status words mean different things, and the difference decides what you are allowed to buy. Superseded means a newer document replaces the old one. Canceled means the document is no longer required, and a notice may recommend a replacement. Inactive for new design means the item may still be bought for existing equipment but must not be designed into anything new.
- A sustaining buyer can keep ordering an AN or MS number that the drawing calls out, as long as the order references the controlling document that now governs it.
- A design engineer starting new work should cite the current NAS, NASM or SAE document, not a canceled or inactive one.
- Status can change by later notice, so check ASSIST or the AIA or SAE catalog at the time of the order, and record the revision you checked.
The definitions above follow MIL-STD-961E; our mil-spec versus commercial parts page covers them in more detail, and our QPL guide covers qualified sources.
Choose AN or MS when, choose NAS or NASM when
Order what the drawing calls out. Choose the document by whether the design is old or new.
Order the AN or MS number when
- The drawing, parts list or illustrated parts catalog calls it out
- The aircraft or system was certified or qualified with that number
- Receiving, kitting and maintenance records are keyed to that number
Choose NAS or NASM documents when
- Engineering is releasing a new design
- The AN or MS document has been canceled and the drawing is being revised anyway
- The application needs close tolerance or high strength features that the NAS family covers, such as the NAS6200 series close tolerance bolts
Cost and availability drivers
Common AN and MS numbers are widely stocked because so much existing equipment uses them. Close tolerance NAS bolts, special finishes, corrosion resistant or titanium versions and low volume dash numbers are thinner on the shelf. Lead time is driven by material, plating, lot size and whether the distributor holds traceable stock under the exact number you ordered. A cross referenced number in stock is not a shortcut unless engineering has approved it.
What to put on the PO
Write the order so the supplier cannot substitute without asking. The list below works for any of the three families.
- Full part number exactly as on the drawing, including material letters, dash numbers and suffixes
- The controlling document and revision, for example NASM21044 for an MS21044 part; where you have not confirmed it, write that the supplier must confirm the current revision on ASSIST or SAE
- No substitution of AN, MS, NAS, NASM or AS numbers without written buyer approval
- Manufacturer name and lot traceability on the certificate of conformance
- Material certs where the part family requires them
- DFARS 252.225-7009 specialty metals compliance on DoD contracts
- Finish restrictions, such as cadmium or hexavalent chromium limits
- Packaging by lot, labeled with part number and lot
Our PO quality flow-down template has clause wording, and our counterfeit parts avoidance page covers buying older numbers safely. Back to the procurement library.
Get AN, MS and NAS hardware sourced to the drawing
Send your hardware list through the hardware request form exactly as it appears on the drawing. We source through authorized and franchised distributors or the manufacturer with traceability, flow down the controlling document and any no-substitution rule, and check the certificate before delivery. A person replies within one business day.
Send the job. A person replies within 1 business day.
Part, quantity and date are enough to start. Drawings and the mutual NDA follow by reply, and controlled programs never send technical data through this site.
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Questions
Is NASM the same part as MS?
Usually the part is the same and only the controlling document changed. AIA converted more than 500 military documents to NAS documents with NASM or NAM prefixes, and parts continue to be procured by their MS part number. For example, MS21044H was canceled and superseded by NASM21044. Order the MS number the drawing shows and cite the NASM document and revision as the controlling specification on the purchase order.
What replaced AN365 nuts?
EverySpec records show AN365 was superseded by MS20365, and MS20365 was in turn superseded by MS21042. In practice, some distributors cross AN365 numbers to MS21044 nuts instead. Those are different documents, so the acceptable replacement for your application is an engineering decision. Use the part number on your drawing or approved alternates list, and do not accept a substitute from a distributor cross reference alone.
Can I use NAS1149 washers in place of AN960?
NAS1149 replaced the AN960 numbering, and distributors list pairs such as AN960C10 with NAS1149C0363R as alternates. An alternate listing is not a certified equivalent. If your drawing or approved data calls out AN960, get engineering approval or an approved alternates entry before substituting. For new design, cite NAS1149 directly so thickness, material and finish are all in the part number.
Where do I check whether an MS standard is still active?
Use ASSIST or its public Quick Search site. DLA describes ASSIST as the official source for specifications and standards used by the Department of Defense, and most unclassified documents can be viewed free. A canceled MS document shows a notice naming any superseding document, often a NASM number. For NAS documents, check the AIA standards catalog. Record the revision and date you checked.
Are AN bolts still allowed?
Yes, where the drawing or approved data calls for them. AN3 through AN20 bolts were canceled by Notice 1 in December 1999 and superseded by NASM3 through NASM20 with identical part numbers, so the part is still bought as AN3, AN4 and so on. What changed is the document that controls it. For new design, cite NASM3 through NASM20 rather than the canceled AN document.
Related
Sources
- Aerospace Industries Association: National Aerospace Standards
- DLA: ASSIST web site details
- DLA: ASSIST Quick Search overview
- Panther Builders Manual: AN, MS, NAS, NASM and AS hardware standards
- EverySpec: AN3 thru AN20 Rev 12 Notice 1, superseded by NASM3 thru NASM20
- EverySpec: MS20365C self-locking nut, superseding AN365, superseded by MS21042
- EverySpec: MS21044H Notice 1, superseded by NASM21044
- EverySpec: MS20470H Notice 1, superseded by NASM20470
- Boeing Distribution: NAS1149 flat washer listing
- Military Fasteners: AN960C10 cross reference
- EverySpec: MIL-STD-961E with Change 4, status definitions
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