Aerospace Fasteners and Hardware: Manufacturing and Supply.

Specifying aerospace fasteners is rarely as simple as picking a part number off the Accu website. International Aerospace standards overlap across decades of military and commercial aerospace history and the right choice for a structural joint depends on fastener family, material grade, thread form, finish and traceability all at once. Get any one of those wrong and the part either won't pass inspection, or won't perform across the years of service life expected for modern aerospace fasteners, potentially with catastrophic outcomes.

This guide breaks this fastener specification problem down in the same way a design or procurement engineer in aerospace manufacturing would resolve it. We'll start with what separates aerospace fasteners from general precision fasteners, then move through the main three governing standards families: AN (Army-Navy), MS (Military Standard) and NAS (National Aerospace Standard).

From there, you'll learn how to decode an AN, MS or NAS part number field by field and how to pick the right alloy for the right zone of an airframe. We'll also cover why aerospace drawings call for UNJ threads and specialist fastener finishes.

Finally, we'll map out how the global aerospace supply chain splits between AS9100 primary sources, aerospace fastener distributors, manufacturers and material-specialist suppliers across the UK, Europe and the US.

Whether you're sourcing for a production aircraft programme, a prototype build or an MRO consumable line, the goal is the same: get the specification right the first time, every time.

Contents:

• What Are Aerospace Fasteners?

• Aerospace Fastener Standards: How AN, MS and NAS Fit Together

• How to Decode an Aerospace Fastener Part Number

• Aerospace Fastener Types and Families

• Aerospace Fastener Materials: Selection by Application

• Thread Forms Fatigue-Critical Joints

• Aerospace Fastener Finishes

• Aerospace Fastener Suppliers, Stockists and Manufacturers

• AS9100, NADCAP and the Aerospace Supply Chain

• Accu's Aerospace Fasteners and Hardware Range

What Are Aerospace Fasteners?

Aerospace fasteners are mechanical fasteners specified to international aerospace standards such as AN (Army-Navy), MS (Military Standard) and NAS (National Aerospace Standard) with material grades, thread forms, finishes and traceability requirements that distinguish them from precision fasteners.

A commercial airliner typically carries between 1.5 and 3 million fasteners and every single one is specified by standard, material and finish the moment it appears on an engineering drawing. Specify the wrong fastener in a critical joint and the consequences scale from "doesn't pass inspection" all the way up to "doesn't survive thousands of pressurisation cycles", which can result in failure.

The gap between aerospace fasteners and the precision screws used in general engineering comes down to specification depth. A DIN 912 cap head screw is defined by dimension and strength grade; an aerospace cap head screw adds an AMS (Aerospace Material Specification) material traceability step to its parent material melt lot, a controlled-root-radius thread form, an aerospace-qualified finish and batch-level documentation that follows the part from initial smelt to airframe.

The sections that follow break down each of those layers: standards, materials, threads, finishes and supply chain, working through them the way a design or procurement engineer resolves them on a custom manufacturing drawing.

Aerospace Fastener Standards: How AN, MS and NAS Fit Together.

Three primary standards families represent three eras of US military and commercial aerospace specification: AN (Army-Navy, 1940s), MS (Military Standard, 1950s onwards) and NAS (National Aerospace Standard, administered by the Aerospace Industries Association since 1941).

All three of these standards are still in use on working drawings across new-production, legacy and maintenance work, setting the standard internationally for aerospace fasteners. Procurement teams in aerospace manufacturing have to read across all three fluently.

Q: Why are all three standard families still live, rather than each one replacing its predecessor?

A: Airworthiness certification is the short answer. Once an aircraft type is approved by the regulator with specific fastener references on its drawings, those references are locked into the type certificate for that aircraft. Re-engineering them means re-qualifying the affected joints, which often costs more than continuing to source the legacy part. This is why a 1965 Cessna 172 carries AN aerospace bolts today in 2026, not because AN is technically superior but because the type certificate says it should.

AN (Army-Navy): The Original Military Fastener System.

The AN (Army-Navy) system originated during the Second World War as a joint US Army Air Forces and US Navy specification to standardise fastener procurement.

AN standards cover bolts (AN3 through AN20 for 3/16" to 1-1/4" diameters), nuts, washers, rivets and turnbuckles. Largely superseded in modern commercial aviation design, an AN bolt remains the standard for piston-era general aviation (Cessna 172, Piper Cherokee families of airframe) and legacy military rotorcraft under original type certificates. MRO (Maintenance, Repair and Overhaul) engineers sourcing an AN bolt for a 1970s airframe regularly work from the original AN-numbered drawing.

The AN numbering scheme runs in 1/16-inch diameter increments. AN3 is 3/16-inch nominal diameter, AN4 is 1/4 inch, all the way up to AN20 at 1-1/4 inches. Once you know the increment is consistent, you can read the diameter of any AN bolt straight off the part number without reaching for a chart.

MS (Military Standard): Expansion and Modernisation.

The MS (Military Standard) system, historically administered by the US Defense Logistics Agency, expanded the AN range with a broader scope covering rivets (MS20470, MS20426), screws, inserts, clamps and military-specific hardware.

Many MS numbers have been superseded by NAS equivalents on commercial programmes, but an MS fastener reference remains authoritative on US defence contracts and across the hundreds of thousands of MS-numbered parts shipping into MRO inventories.

MS numbers are organised in application-grouped blocks. Spotting the block in the leading digits tells you the category of part before you read the rest of the number giving you the fastener specifics. We'll show you how to decode a full MS part number later in the guide.

NAS (National Aerospace Standard): The Current Industry Authority.

The National Aerospace Standard system has been administered by the Aerospace Industries Association (AIA) since 1941 and is the dominant specification authority on new commercial aerospace designs. NAS covers structural bolts, airplane screws, pin-and-collar fasteners, lockbolts and over a thousand other component types. A new Airbus or Boeing structural drawing issued today is overwhelmingly NAS-numbered, a demonstration of the international nature of the standard.

Like MS, NAS uses application-grouped blocks, though the conventions are messier and a little harder to decode. We'll show you how to read a full NAS part number in the next section. These are the standards we see specified most in modern aeroplane fastener manufacture.

Metric Aerospace Fastener Standards.

All of the standards covered above are imperial in origin. For metric aerospace work, a parallel family exists. The EN (European Norm) aerospace series administered by ASD-STAN is the dominant modern metric family on Airbus programmes and across the European aerospace supply base. Historic national standards like LN (Luftfahrt-Norm, Germany) and NSA (Aerospatiale, France) still appear on legacy European drawings.

EN numbering doesn't decode the way AN, MS or NAS numbering does. An EN part number like EN 6114 is a reference into the standards catalogue rather than a field-delimited string carrying dimensional information.

ASD-STAN: To find out what an EN-numbered part actually is, read the corresponding ASD-STAN specification sheet rather than try to parse the number. ASD-STAN's full standards catalogue is publicly available and no decoding is needed to understand what a part is.

ASD-STAN Spec Sheets

Other Prefixes You'll See On Aerospace Drawings.

AN, MS and NAS aren't the only prefixes you'll see on aerospace drawings. Modern Boeing and Airbus drawings can also feature four other prefixes that are common enough to be essential knowledge for aerospace engineers.

AS (Aerospace Standard): the umbrella standards family for aerospace, with roots in SAE's long-running aerospace standardisation work going back several decades.
It's a deceptively broad prefix: AMS material specifications, the AS9100 quality management standard, hardware references like AS568 for O-ring sizes and a range of process and inspection standards all fall under it. In modern aerospace, AS9100 is the quality baseline for production supply, AMS specs control fastener materials on virtually every commercial airframe drawing. If a four-digit AS number appears on a drawing, the safe assumption is that it's a SAE-administered standard rather than a fastener part number directly.

AS Specification Sheets.

MIL-DTL (Military Detail Specification): the modern US military specification prefix, introduced to replace the older MIL-S prefix in a Department of Defence (DoD, more recently the Department of War) standardisation effort in the late 1990s. The rename was part of broader DoD acquisition reforms that simplified the military specifications system, but MIL-S references still appear on legacy drawings under the same parallel-live pattern as AN references. 

In modern usage, MIL-DTL is the prefix to look for on current US defence procurement, military aircraft production drawings and US military MRO inventories. Spotting a MIL-S on a drawing usually means you're looking at a legacy specification that may have a current MIL-DTL equivalent worth verifying.

MIL-DTL Specification Sheets.

BAC (Boeing Aircraft Configuration): Boeing's proprietary specification prefix, used internally and on Boeing engineering drawings across the company's long commercial aircraft history. The prefix covers anything where Boeing's own engineering team wanted tighter or different control than the standards bodies provided: company-specific surface finishes, in-house designed brackets, design conventions and process standards.

In modern usage, any Boeing commercial drawing across the 737, 747, 777 and 787 families is likely to cite at least a handful of BAC references alongside the NAS structural callouts. Recognising a BAC prefix immediately tells you that the spec is Boeing-controlled and not available through standard specification drawing portals and aerospace supply chains.

ABS (Airbus Standard): Airbus's proprietary equivalent of BAC, used internally and on Airbus engineering drawings across the company's commercial aircraft programme. It covers the same kind of company-specific scope as BAC: Airbus-developed processes, design specifications and configuration items that go beyond what NAS, MS or AS cover.

In modern usage, expect to find ABS references on any drawing from the A320, A330, A350 or A380 programmes. Like BAC, an ABS-numbered spec is controlled by Airbus engineering and the source document won't appear in the standard public portals.

A real-world commercial aerospace drawing can cite a NAS bolt, an AS9100 traceability requirement, a BAC surface finish and an MS-numbered washer all on the same page. Depending on the age of the aircraft and the nature of the work involved, MROs on older airframes will typically see more than one standard referenced.

How to Decode an Aerospace Fastener Part Number.

Now that we've mapped out how AN, MS and NAS standards fit together, let's see what these part numbers look like when broken down for real-world components.

Aerospace part numbers encode specification, size, length, material and finish in a compact alphanumeric string. Every AN, MS and NAS part number follows a field-delineated convention tied to its governing specification. Once the grammar is clear, sourcing and selecting fasteners becomes non-ambiguous, which is why aerospace assembly drawings still list parts by number rather than by description.

Reading an AN Part Number: AN3-10A Aircraft Machine Bolt.

AN part numbers follow a consistent grammar across the whole family: prefix, then diameter code in 1/16-inch increments, dash, then grip length in 1/8-inch increments, then any suffix letters indicating installation features. The increments are fixed across every AN bolt on the books, which is what makes the grammar genuinely transferable. Once you know it, you can decode any AN number cold without a chart.

For example, an AN3-10A bolt is a general-purpose aircraft hex-head bolt with an undrilled shank, specified for use with a self-locking nut rather than a castellated-nut and cotter-pin arrangement.

Applied to AN3-10A:

• AN: Army-Navy specification family.

• 3: Nominal diameter in 1/16-inch increments, so 3/16". The same rule gives 1/4" for AN4 and 1-1/4" for AN20.

• 10: Grip length in 1/8-inch increments. 10/8" = 1-1/4".

• A: suffix letter indicating an undrilled shank.
  The default AN bolt (no letter suffix) has a drilled shank for castellated-nut and cotter-pin safetying. Adding "A" specifies an undrilled shank for use with a self-locking nut instead. A separate "H" suffix (placed after the AN number, e.g. AN3H) indicates a drilled head for safety wire.

Thread length is not encoded in the part number because it is a fixed constant per bolt diameter defined in the specification. Every AN3 bolt has the same thread length regardless of dash number.

Since thread length is fixed, specifying the grip length implicitly defines the total bolt length, grip plus the fixed thread length for that diameter.

Thread length for each diameter is published in the AN specification sheet for each fastener family.

AN specification sheets are held as military documents on the ASSIST standardisation portal. The original AN3 through AN20 bolt specification has been formally superseded by NASM3 through NASM20, published by the Aerospace Industries Association through IHS Engineering Workbench, though the AN-numbered originals remain the working reference on legacy type certificates.

AN-ASSIST Specification Sheets

Reading an MS Part Number: MS20470AD4-6.

MS part numbers don't follow a single grammar convention the way AN numbers do. Each fastener family uses its own rules, so the convention that decodes a rivet number won't necessarily decode an MS-numbered screw, nut or insert.
The common thread is that every MS part number opens with the specification number, which identifies both the component type and the application block it belongs to. Once you know the specification you are checking against, the rest of the number reads against that specification's own field structure.

The following example uses an MS20470 solid universal-head aluminium rivet to show how the fields break down.

For the MS20470 rivet family, the pattern reads: specification number, alloy code letters, diameter in 1/32-inch increments, dash, overall rivet length in 1/16-inch increments.

Applied to MS20470AD4-6:

• MS20470: solid universal-head rivet specification.

• AD: T4 aluminium alloy, the industry standard aerospace rivet material.

• 4: diameter in 1/32-inch increments, so 4/32" or 1/8".

• 6: overall rivet length in 1/16-inch increments, so 6/16" or 3/8". This is the total length of the rivet before installation, not the grip thickness of the joint.

The full part is a 1/8"-diameter by 3/8" long T4 universal-head solid rivet.

AD (T4 Aluminium) is the most commonly specified alloy code, but MS20470 covers several other aluminium and titanium alloy options, each with its own storage and installation requirements. The full alloy code table and dimensional specifications are published in the MS20470 specification sheet, available through ASSIST.

ASSIST (US Department of Defence standardisation portal): holds current and superseded MIL and MS documents, including the MIL-DTL family and historical MIL-S references. Many documents are publicly downloadable without a subscription, which makes ASSIST the easiest first-stop check for military specifications.

MS-ASSIST Specification Sheets

Reading a NAS Part Number: NAS1351-4-8.

NAS part numbers like MS don't follow a single code system either; each fastener family uses its own field structure, so the convention that decodes a socket head cap screw won't necessarily decode a hex head bolt or a Hi-Lok pin. The common thread is that every NAS part number opens with the specification number, which identifies the component type. Once you know the specification, the rest of the number reads against that specification's own coding table.

The following example uses a NAS1351 alloy-steel socket head cap screw to show how the fields break down. NAS1351 is the aerospace equivalent of an industrial DIN 912 cap head screw, built to tighter material and traceability standards.

For the NAS1351 family, the pattern reads: specification number, dash, thread size code (outlined per the specification), dash, nominal length in 1/16-inch increments.

Applied to NAS1351-4-8:

• NAS1351: socket head cap screw specification, alloy steel.

• 4: thread size code. On NAS1351, the first dash number maps to a thread size via a table in the specification rather than a direct dimensional calculation. Code 4 = 1/4-28. The thread form is specified per MIL-S-7742, which governs the controlled-root-radius geometry covered in the thread forms section further down.

• 8: nominal overall length in 1/16-inch increments, so here this is 8/16" or 1/2".

The full part is a 1/4-28 socket head cap screw, alloy steel, 1/2" long, manufactured to NAS1351.

Additional codes in the NAS1351 family designate material (C for corrosion-resistant steel), head type (H for drilled head), locking element and finish. The full coding table and dimensional specifications are published in the NAS1351 specification sheet, available through IHS Engineering Workbench.

IHS Engineering Workbench (now part of S&P Global): the licensed source for current and historical NAS documents. A subscription is required for full access, which is why most aerospace primary suppliers hold an enterprise licence rather than buying documents per lookup.

AIA-NAS Specification sheets

AN/MS/NAS Cross-Reference.

The same fastener application often has multiple part numbers in the same or across different aerospace fastener standards, particularly for general structural hardware. The table below shows where some common applications have direct equivalents and where they don't across AN, MS and NAS standards. This table is not exhaustive and should be seen as an example when comparing standard families as to what you can expect to see.

An MRO engineer servicing a 1970s-type certificate will find AN-numbered fasteners on the original drawings. The AN specification has been formally superseded by NASM (AN3 through AN20 became NASM3 through NASM20), but the part numbers and dimensions are identical. 
The practical cross-referencing challenge comes when a drawing calls an obsolete AN rivet, such as AN470 (now MS20470), where the specification number changed between families, or when the engineer needs to determine whether a higher-specification NAS part can substitute on a given application. Getting the substitution wrong is a non-conformance against the type design data and an airworthiness issue.

Aerospace Fastener Types and Families: Bolts, Screws, Rivets, Hardware and Captive Fasteners.

Aerospace fasteners broadly split into six primary families: aircraft bolts, close-tolerance shear bolts, aircraft screws, interference-fit pin-and-collar fasteners, rivets and captive fasteners.

Each family exists because it solves a different structural problem and a single airframe drawing typically calls out all six alongside general aircraft hardware (also referenced as aerospace hardware) such as washers, castellated nuts and clip fasteners. The table below maps each family to its governing standard, typical aircraft application zone and the identifying features that distinguish one from another on a drawing or online.

Exploring Specific Aerospace Fastener Types.

Aircraft Hex Head Bolt (AN3-AN20, NAS6603, MS9559).

Aircraft hex head bolts appear throughout the airframe structure wherever a removable bolted joint is specified.
The AN3-AN20 family (NASM3-NASM20) at 125 KSI (thousand pounds per square inch) is the general-purpose version, typically safetied with a castellated nut and cotter pin via a drilled shank.
NAS6603 at 160 KSI is the close-tolerance upgrade, primarily specified on shear-critical joints with self-locking nuts. Both carry AMS-specified material traceable to melt lot and head stamps identifying the manufacturer and standard. A DIN 933 hex bolt carries none of those features.

Close-Tolerance Bolt (NAS6203, NAS1303).

Close-tolerance bolts are specified on shear-critical joints where fatigue life depends on eliminating movement between the bolt and the surrounding material. The bolt shank is precision-ground to h6 tolerance, so it bears directly against the hole wall rather than relying on thread clamp-up alone.

These sit in wing spar joints, control-surface hinge brackets and anywhere cyclic shear loading would otherwise initiate fatigue cracking at a clearance-fit hole. NAS6203 and NAS1303 are the governing specifications; these are not catalogue parts and are typically produced to drawing through a custom manufacture route.

Aircraft Screw (MS24694, NAS1351).

Aircraft screws cover secondary structure, panel attachments and non-primary assemblies across the airframe. NAS1351 specifies a hex socket head cap screw in alloy steel; MS24694 covers countersunk-head screw variants. The aerospace versions differ from a standard DIN 912 cap head screw in the same ways as aircraft bolts: AMS material specification, controlled thread form and batch-level traceability that a commercial-grade fastener does not carry.

Hi-Lok Pin and Collar (NAS1669 / NAS1670).

Hi-Lok fasteners are two-piece pin-and-collar systems specified on interference-fit structural joints across wings, fuselage and empennage.
The NAS1670 collar shears off at a calibrated torque, making the installation self-gauging: if the collar hex is gone, the preload is correct. This removes operator variability and the torque-wrench inspection step used on conventional structural bolting. Hi-Lok was originally developed by Hi-Shear Corporation in the 1960s and is now produced under license by multiple aerospace fastener manufacturers. Adoption accelerated through military programmes from the late 1970s onward.

NAS Lockbolt (NAS1738).

Lockbolts serve the same structural role as Hi-Lok fasteners but are specified where access is limited to one side of the joint. A swaged collar locks onto the bolt shank via a shear-ring groove, forming a permanent interference-fit joint.
These sit in fuselage skin-to-frame joints, wing skin panels and other high-cycle structural applications where single-side installation is a production or maintenance requirement.

Solid Rivet, Universal Head (MS20470).

MS20470 universal-head solid rivets in 2117-T4, 2024-T3 or 5056-H32 aluminium alloy remain the dominant structural fastener on aluminium airframes built before the composite transition. The dome head sits proud of the skin surface and is used across internal structure and non-aerodynamic external surfaces. Most 737 Classic and 737 Next Generation skin structure is riveted rather than bolted and a 35-year airframe on its second D-check still consumes these rivets in the tens of thousands per overhaul.

Solid Rivet, Countersunk (MS20426).

MS20426 countersunk solid rivets use the same aluminium alloy grades as MS20470, but with a 100° countersunk head that sits flush with the skin surface. These are specified on leading edges, external skin panels and any aerodynamic surface where a protruding head would create drag. The alloy codes and specification discipline are identical to MS20470; the only difference is head geometry, driven by where on the airframe the rivet sits.

Cherry Blind Rivet (NAS1398, NAS1399).

Cherry Aerospace's blind rivet families are specified wherever the back side of an airframe joint is unreachable for conventional solid-rivet installation. CherryMax and CherryLOCK are the two primary product lines, specified across NAS1398 and NAS1399.
These sit on access panels, door surrounds and interior structural joints where single-side access is a production or maintenance constraint. What separates them from a standard blind rivet is that they are rated for structural shear and tensile loads rather than panel retention alone.

Captive Fastener (NAS1473, MS21059).

Captive fasteners are permanently fixed to one side of a structure so the mating bolt or screw can be installed and removed repeatedly without access to the blind side. The most common form is the floating anchor nut to NAS1473 or MS21059, specified on access panels, removable inspection covers and avionics-bay structure.

The boundary between aerospace fasteners and electronics hardware is most visible in avionics bays, where captive fasteners provide serviceable mounting for line-replaceable units and the precision hardware around aerospace contacts in MIL-spec connector assemblies. Where rivet retention of an anchor nut is impractical in a thin sheet structure, self-tapping threaded inserts deliver a similar captive function in a smaller envelope.

Aerospace Fastener Materials: Selection by Application.

Once you know the standard and the part number, the next question is what material the fastener is made from. The ideal fasteners for any given zone depend on the operating environment: temperature, corrosion exposure, cyclic loading and galvanic compatibility with the surrounding structure.

Aerospace fastener material selection is zone-driven and this level of material discipline is what distinguishes aerospace engineering manufacturing from general industrial practice. Every material is specified by an AMS (Aerospace Material Specification) number and carries batch-level certification traced back to the melt lot.

Structural Airframe Fasteners: Titanium (Grade 5).

Titanium is a lightweight, corrosion-resistant transition metal with an exceptionally high strength-to-weight ratio. Grade 5 (Ti-6Al-4V) is the most widely used titanium alloy in aerospace, containing 6% aluminium for strength and 4% vanadium for ductility. It is specified under AMS 4928 in the annealed condition, delivering roughly 950 MPa ultimate tensile strength at around 56% of the density of steel.

Ti-6Al-4V is the structural airframe material of choice wherever weight saving and galvanic compatibility with composite structure matter equally. Unlike aluminium or cadmium-plated steel, titanium sits close to carbon fibre in the galvanic series and doesn't corrode when the two are in contact. This makes it the ideal fastener material for composite-to-metal structural joints on CFRP-intensive airframes like the 787 and A350. Titanium fastener consumption has grown with every composite-intensive programme as CFRP primary structure has replaced aluminium across the commercial fleet.

Accu holds a stocked range of Grade 5 titanium screws from M2 to M10. For deeper material context, see our engineer's guide to titanium.

Hot-Section and High-Temperature Fasteners: A286 (AMS 5731) and Inconel 718 (AMS 5662).

A286 is an age-hardenable, iron-nickel-chromium superalloy (AMS 5731) that holds useful fastener strength to approximately 650°C, placing it in turbine-engine accessory sections and hot airframe structure elements.

Inconel 718 is a nickel-chromium-based superalloy (AMS 5662) that extends the ceiling to roughly 700°C and has been specified historically on applications as demanding as rocket-engine turbopump bolting.

Both are chosen where standard alloy steel or stainless steel would lose yield strength well below the operating temperature of the section in question. Accu stocks A286 screws and other fasteners across a range of metric sizes; for Inconel 718 requirements, our custom manufacture route can supply against your technical drawings.

Corrosion-Critical Structural Fasteners: 17-4PH.

17-4PH is a martensitic precipitation-hardening stainless steel and one of the most widely specified corrosion-resistant structural alloys in aerospace. The designation describes its composition: 17% chromium for corrosion resistance and 4% nickel for toughness, with copper and niobium additions that enable the precipitation-hardening response. It is specified under AMS 5643 for bar and forging stock.

The PH (precipitation-hardening) mechanism works by age-hardening the alloy after solution treatment. Heating to a controlled ageing temperature precipitates copper-rich particles within the steel matrix, which pin dislocations and deliver high strength. Different ageing temperatures produce different property balances: H900 condition gives the highest tensile strength for maximum load-bearing, H1025 and H1075 balance strength with improved toughness and H1150 gives the best ductility for applications where impact resistance matters more than peak strength.

The result is a material that combines stainless-steel corrosion resistance with near-alloy-steel structural strength, making it the standard choice for landing gear pin joints, hydraulic fittings and marine-environment structural brackets where cadmium-plated alloy steel carries unacceptable salt-spray corrosion risk. 17-4PH is chosen over standard austenitic stainless steels (304, 316) wherever the application needs both corrosion resistance and structural load-bearing capability.

See Accu's stainless steel types, grades and finishes for full 17-4PH material details and the 17-4PH fasteners stocked range.

General Structural and Secondary Fasteners.

Alloy steel to AMS 6322 or AMS 6415 (4340 family) is the workhorse structural fastener material across aerospace and has been since the earliest stressed-skin aircraft designs.
4340 is a nickel-chromium-molybdenum alloy steel: the nickel adds toughness, chromium adds hardenability and wear resistance, molybdenum adds high-temperature strength and resistance to temper embrittlement. The alloy heat-treats to tensile strengths in the 180 to 200 KSI range, making it the standard for high-strength structural bolting where the galvanic, thermal or corrosion demands of the application don't require titanium, 17-4PH or a superalloy. Alloy steel fasteners are typically finished with cadmium plating (legacy) or IVD aluminium (current) for corrosion protection, since the base material has no inherent corrosion resistance.

7075-T6 aluminium (AMS-QQ-A-367) is a zinc-alloyed aluminium with copper and magnesium additions, heat-treated to the T6 temper for peak strength. It covers secondary structure, access panels and non-flight-critical brackets where moderate strength at roughly one-third the density of steel matters more than absolute tensile capability. The limitation on modern composite airframes is that 7075-T6 is cathodic to carbon fibre: placing an aluminium fastener in contact with CFRP creates a galvanic cell that corrodes the aluminium, which is why titanium has largely replaced it for composite-to-metal joints on programmes like the 787 and A350.

Thread Forms for Fatigue-Critical Joints.

Material selection provides the right alloy for a joint, housing or structural components. Thread form and finish determine how that joint performs under decades of cyclic loading and intense vibration.

Controlled-Preload Installation and Tightening Strategies.

Aerospace structural joints require controlled preload, not just controlled torque. Under-preloading can cause the joint to fatigue prematurely at the thread root; over-preload and the bolt yields, reducing the fatigue life that the thread form is designed to deliver.

Three installation methods dominate:

• Torque-and-angle: tighten to a specified torque, then rotate an additional specified angle. The angle step overrides the friction variability that compromises torque-only readings.

• Torque-to-yield: tighten until measurable yield onset. Used on selected high-fatigue applications; yield-cycled bolts are typically single-use due to the nature of their installation, resulting in deliberate deformation of the bolt.

• Self-gauging shear-collar: the collar on a Hi-Lok or NAS lockbolt shears off at calibrated torque values, eliminating the torque-wrench inspection step entirely. This is the dominant method on modern production airframes because it removes preload guesswork at scale.

UNJ thread forms and controlled-preload installation are complementary. UNJ raises the fatigue ceiling of the joint and controlled installation ensures that the ceiling is reached without overshoot.

The UNJ Controlled-Root-Radius Thread (MIL-S-8879).

The development of controlled-root-radius threading was a significant fastener innovation technology milestone in post-war aerospace. UNJ threads are a Unified Imperial thread variant with a controlled root radius specified under MIL-S-8879. Standard UN threads permit a flat or variably radiused root; UNJ mandates a larger, precisely controlled radius that reduces stress concentration at the thread root, the site of peak stress under tensile cyclic loading.

The practical result is component fatigue-life improvements of three to four times over equivalent UN threads making UNJ the default on fatigue-critical structural bolting for aerospace fasteners. UNJ thread forms are available through Accu's custom manufacture route for drawing-specific aerospace fastener requirements.

Aerospace Finishes: Cadmium, Passivation and IVD Aluminium.

Aerospace finishes aren't cosmetic and are usually integral to the fastener's use case. They add functional properties on top of the fastener parent material. The finish specification on an aerospace drawing is as tightly controlled as the material callout itself.

• Cadmium plating (AMS-QQ-P-416): the traditional aerospace finish, providing sacrificial-anode corrosion protection and thread lubricity on alloy-steel fasteners.
  Cadmium has been the default on military and commercial programmes for decades, but it is a REACH Annex XVII restricted substance (due to being carcinogenic) and European commercial programmes have been driving a structured phase-out since the late 2000s.
  Cadmium is still specified on legacy military drawings and some US programmes but is increasingly replaced by IVD (Ion Vapour Deposition) aluminium on new commercial work.
  
  

• Passivation (AMS 2700): a nitric or citric acid treatment that removes free iron from the surface of corrosion-resistant steels, standard on 300-series, 400-series and 17-4PH stainless steel fasteners.
  Unlike cadmium, passivation isn't a coating. It enhances the natural chromium oxide layer that gives stainless steel its corrosion resistance. Widely used across aerospace and general engineering and not subject to any phase-out.
  
  

• IVD Aluminium (AMS 2454): Ion Vapour Deposition aluminium is the modern cadmium replacement on new commercial aerospace programmes. A vacuum-deposited aluminium coating that delivers comparable galvanic protection and thread lubricity without the toxicity concerns. IVD is increasingly the specified alternative on new Airbus and Boeing commercial programmes where cadmium would previously have been called out.

The European REACH regulation's restrictions on cadmium have driven one of the largest finish-specification changes in commercial aerospace history. Airbus and its tier-one supply chain have been transitioning cadmium-plated part numbers to IVD aluminium alternatives since the late 2000s, a change that touches every alloy-steel fastener on the production line and cascades through the entire upstream supply chain.
The transition is still ongoing because each finish change must be qualified and approved by the OEM as a minor design change under their type certificate authority, working through the affected part numbers one by one rather than as a blanket regulatory switch.

Aerospace Fastener Suppliers, Stockists and Manufacturers.

When you've identified the standard, decoded the part number and confirmed the material and finish, the final question is who supplies the part. The answer depends on what the drawing calls for and what stage the programme is at.

Aerospace fastener supply splits across four layers. Each serves a different stage of the procurement cycle:

If your drawing mandates AS9100 flow-down on the line item, you need an AS9100-certified aerospace fasteners stockist or manufacturer with the relevant NADCAP accreditations. These are the aircraft hardware suppliers and aerospace hardware distributors that production programmes source from directly. The aircraft fasteners international market is concentrated around a small number of global primary suppliers and their licensed aerospace fastener distributors across the UK, Europe and the US.

If the drawing calls for a specialist aerospace-grade material in prototype, qualification or low-volume quantities, a material-specialist aerospace supplier is the fit. Accu sits in this tier: aerospace-grade materials and aerospace supplies stocked to precision quantities, plus a custom manufacture route for drawing-specific parts covering UNJ thread forms, specialist materials and specialist finishes.

Tier-one aerospace fastener companies typically quote minimum order quantities of 10,000 to 100,000 parts per line, which a prototype or qualification build rarely justifies. Accu offer sourcing on component quantities as low as a single fastener. The best aerospace component suppliers for this kind of work sit in the material-specialist tier.

Most mature aerospace manufacturing programmes run both routes in parallel: an AS9100 aerospace fasteners supplier for the production catalogue parts and a material-specialist partner like Accu for the low quantity prototype, qualification and custom-manufacture work alongside it.

AS9100, NADCAP and the Aerospace Supply Chain.

AS9100 is the aerospace-specific extension of ISO 9001, published by the International Aerospace Quality Group (IAQG), currently at Revision D (2016 release) as of Spring 2026. It is the baseline quality-management standard for primary aerospace supply across civil, military and space applications.

AS9100: What It Covers Beyond ISO 9001.

AS9100 Rev D builds on ISO 9001:2015 with aerospace-specific clauses covering risk-based configuration management, product safety, counterfeit-part prevention, First Article Inspection (FAI) per AS9102, operational risk management and traceability and non-conformance control.

A supplier holding ISO 9001 alone cannot meet AS9100-mandated line items without additional qualification, because the aerospace clauses are not in the ISO 9001 scope.

NADCAP: The Special Process Layer.

NADCAP (National Aerospace and Defence Contractors Accreditation Program) operates at a process-specific layer rather than supplier-wide. Audited NADCAP special processes include heat treatment, chemical processing (anodising, passivation, cadmium plating), non-destructive testing (NDT), welding, brazing and coatings. A supplier can be AS9100 certified without NADCAP accreditation and a NADCAP heat-treatment accreditation does not confer AS9100 certification.

Accu holds ISO 9001:2015 quality management, audited by Bureau Veritas. Accu does not hold AS9100 certification and this guide does not claim otherwise.

For programmes where AS9100 primary supply is mandated by drawing or contract, Accu operates as a materials specialist and custom manufacturing partner alongside an AS9100 primary source, manufacturing aerospace-specification parts to drawing through our custom manufacturing process. A Certificate of Conformity ships as standard on every order; EN 10204 3.1 mill certification is available on request.

Accu's Aerospace Fasteners and Hardware Range.

Accu supplies our fasteners in aerospace-grade materials and a custom manufacture route tailored to drawing-specific aerospace fastener specifications. The table below shows our stocked aerospace material families and where to find them on the site.

Why engineers choose Accu for aerospace-grade components:

• Custom manufacture from £250 for drawing-specific parts: UNJ thread forms to MIL-S-8879, specialist materials and specialist finishes without tier-one minimum-order-quantity constraints.

• Specialist finishes including AccuBlack, AccuLock (pre-applied thread-locking patch), Precote 80 and Anu-Lok 180.

• ISO 9001:2015 quality management audited by Bureau Veritas. Certificate of Conformity ships as standard on every order. EN 10204 3.1 mill certification available on request.

• Free 3D CAD model downloads from every product page across a fully searchable online aerospace fastener catalogue covering 750,000+ SKUs.

 

Wrapping Up Aerospace Fasteners and Hardware.

Aerospace fastener and aircraft hardware specification is a four-layer problem: family, standard, material and finish.
The right supplier depends on where the drawing sits across those layers. For drawing-specific NAS, MS or AN parts on a primary aerospace supply line, an AS9100 stockist-distributor is the correct fit.
For aerospace-grade materials in precision quantities, prototype-to-qualification volumes and custom manufacture from £250 against drawing, Accu is the fit.
Most mature aerospace manufacturing programmes run both routes in parallel. 

Further Reading.

• An engineer's guide to titanium: grade-by-grade properties from Grade 1 commercially-pure through Grade 5 Ti-6Al-4V.

• Stainless Steel Types, Grades and Finishes: reference covering A2, A4, Duplex, BUMAX and 17-4PH.

• ISO 9001 Quality Management System: Accu's Bureau Veritas-audited quality management system.

 

Frequently Asked Questions.

Q: What are aerospace fasteners?

A: Aerospace fasteners (also commonly referenced as aviation fasteners, aviation hardware or aircraft fasteners) are mechanical fasteners specified to aerospace standards (AN, MS, NAS) with material, thread, finish and traceability controls that exceed general industrial fastener specifications.
A commercial airliner carries between 1.5 to 3 million of them, each one specified by engineering drawing and certified against an AMS material specification with an audit trail back to the melt lot.

Q: What's the difference between AN, MS and NAS fasteners?

A: AN (Army-Navy), MS (Military Standard) and NAS (National Aerospace Standard) represent three overlapping eras of US aerospace fastener specification. AN dates from the 1940s, MS expanded from the 1950s under US Defense Logistics Agency administration, NAS has been run by the Aerospace Industries Association since 1941 and dominates new commercial design. All three remain in use on working drawings.

Q: What role do fasteners play in aerospace manufacturing?

A: Aerospace fasteners are the primary mechanical joining method in aerospace manufacturing assembly across airframe structure, engine accessory sections, landing gear and avionics bays. Fastener selection drives weight, fatigue life and galvanic compatibility across the airframe.

Q: What are aircraft bolts usually manufactured with?

A: Aircraft bolts are typically manufactured from high-tensile alloy steel or specialized aerospace alloys, such as Grade 5 Titanium, A286, Inconel 718 and 17-4PH precipitation-hardening stainless steel.

To maximise fatigue life, the threads are cut to a controlled-root-radius (UNJ form per MIL-S-8879) and rolled after heat treatment to introduce residual compressive stress at the root. For added security, the head or shank is frequently drilled to accommodate safety wire or a castellated nut and cotter pin.
Strict quality control requires component head stamps to identify the manufacturer and governing standard, alongside full material certification traceable back to the original mill heat.

Q: Where can I find an aerospace fastener catalogue?

A: Aerospace fastener catalogues are published by specialist aerospace fasteners manufacturers (LISI Aerospace, Howmet Aerospace, Cherry Aerospace) and AS9100 certified aerospace fastener distributors holding catalogue-line NAS, MS and AN inventory.
For aerospace-grade material stocked to precision quantities rather than NAS-numbered catalogue lines, Accu offers a fully online fastener selection covering Grade 5 Titanium, 17-4PH, BUMAX and Duplex.

Q: What are captive fasteners in aerospace applications?

A: Captive screws in aerospace applications are screws retained in the panel or structure so they cannot be lost during removal. The screw lifts clear of the mating thread when unfastened but remains captured in the panel by a retaining ring or spring clip. This prevents foreign object debris (FOD) in safety-critical areas and speeds up repeated access during scheduled maintenance. Captive screws dominate access panels, removable inspection covers and avionics-bay structure across both commercial and military airframes.

Q: Where can I get speciality fasteners for aerospace applications?

A: Speciality aerospace fasteners are split into two routes. NAS, MS and AN catalogue parts come from AS9100 stockist-distributors with aerospace traceability. Drawing-specific parts in specialist materials or non-standard thread forms (UNJ, specialist finishes) come from a custom manufacture route such as the one that Accu offers. 

Q: Does a supplier need AS9100 certification to ship aerospace fasteners?

A: For direct supply into a production aircraft programme against a drawing with AS9100 flow-down, yes: AS9100 requirement has to be met.
For prototype, qualification, R&D, student and motorsport adjacent work, ISO 9001:2015 with EN 10204 3.1 material certification is routinely acceptable.
Mature aerospace manufacturing programmes dual-source across both supplier types.

Q: Why do aerospace drawings specify UNJ threads instead of UN threads?

A: Aerospace drawings specify UNJ threads (MIL-S-8879) over standard UN threads on fatigue-critical joints because UNJ mandates a larger, controlled root radius proportional to the thread pitch. This larger radius reduces stress concentration at the thread root, which is the peak-stress site under cyclic tensile loading. Published fatigue-life improvements of three to four times over UN make UNJ the default across aerospace structural bolting.

Q: Can a standard 12.9 high-tensile bolt substitute for an aerospace-grade fastener?

A: No. A 12.9 cap head screw (DIN 912, ISO 4762) meets dimensional and mechanical requirements to ISO 898-1 but lacks the AMS material specification, controlled UNJ thread form, aerospace finish and batch-level traceability an aerospace fastener drawing requires.
Substituting a 12.9 bolt on an aerospace drawing is a non-conformance, regardless of how closely the nominal strength figures match, as the lack of certification is itself the issue.