Aerospace Bolts and Screws: Specs, Part Numbers and Buying

Updated October 12, 2026

Bolt and screw families and where they are used

Most structural threaded fasteners on aircraft, launch vehicles and ground equipment come from a short list of AN, MS, NAS and NASM standards. FAA Advisory Circular 43.13-1B groups aircraft bolts into general purpose, internal wrenching and close tolerance types, and warns that bolts made to a special part number must be replaced with like bolts. The table lists the families buyers see most often, using the descriptions in AC 43.13-1B Table 7-12 and the related paragraphs.

AC 43.13-1B paragraph 7-41 adds two limits worth putting in front of any designer reusing old hardware lists: steel bolts smaller than No. 10-32 and aluminum alloy bolts smaller than 1/4 in should not be used in primary structure, and aluminum bolts or nuts should not be used where the joint is removed often for inspection or maintenance.

The specifications that govern bolts and screws

The part standard (AN, MS, NAS or NASM) defines the geometry and calls out the material and finish specifications. Status matters because a cancelled document often keeps its part numbers alive under a new owner. The statuses below are the ones we could confirm in the cited sources; check DLA ASSIST or the issuing body for anything else before you write the PO.

One quirk with cadmium: when SAE adopted the federal spec it restarted the revision letters, so AMS-QQ-P-416 revision A is not older than QQ-P-416F. Write the full document number and revision letter rather than relying on the letter alone. Plating and coating callouts are covered in more depth on the surface finishing page.

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How the part number is built

Two common families decode cleanly from published data, and both show why you order by the full number and never by a description.

AN3-5A

• AN3: the diameter code. AN3 is the No. 10 (3/16 in) bolt with 10-32 thread. Larger codes step up in sixteenths of an inch.
• Material letter: none here, which means cadmium plated alloy steel. A C after the AN number means corrosion resistant steel and DD means aluminum alloy.
• H after the AN number (absent here): a head drilled for safety wire.
• -5: the length code. For single digit dash numbers on AN3 and AN4 bolts, the published rule is the dash number in eighths of an inch plus 1/32 in, so -5 gives 21/32 in overall. The DLA fastener catalog lists AN3-5A at 0.656 in length and 0.250 in grip.
• A: undrilled shank, so the bolt is meant for a self-locking nut rather than a castle nut and cotter pin.

Even this simple number has a trap: a distributor table lists the AN3-5 grip as 7/32 in, while the DLA catalog says 0.250 in. AC 43.13-1B recommends measuring the bolt being replaced instead of trusting a parts list, because fastener specifications have changed over the years.

NAS6203-26

• NAS62: hex head, short thread, alloy steel, close tolerance series.
• 03: the diameter in sixteenths, so 3/16 in, listed as 0.190 in nominal thread diameter. NAS6204 is the 1/4 in bolt.
• -26: the grip in sixteenths of an inch. Boeing Distribution lists NAS6203-26 with a grip of 1.615 to 1.635 in, which is 26/16 in nominal.
• X or Y after the dash number: AC 43.13-1B paragraph 7-49 says NAS6200 series bolts come in two oversized grip diameters for slightly elongated holes, for example NAS6204-6X for a 1/4 in bolt with a 1/64 in larger shank. The hole may need reaming to fit.

Grip length, thread form and head styles

Grip is the thickness of material the bolt is designed to hold. AC 43.13-1B paragraph 7-37 allows a slightly longer grip if washers go under the nut or head, but caps the combined washer height at 1/8 in, which in practice limits you to the next standard grip size. Every bolt and nut installation should show at least one full thread through the nut. For plate nuts, the AC says to shim under the plate if the right grip is not available.

Aerospace bolts are usually threaded to the UNJ profile in SAE AS8879. The defining feature is a controlled root radius on the external thread, with enlarged minor diameters on both the external and internal threads to make room for that radius. The standard covers nominal diameters from 0.060 to 6.000 in, thread classes, tolerances and how threads are designated. Distributor listings for NAS6203 bolts show a class 3A thread, the tight commercial class. If your drawing calls UNJ, do not accept a commercial UN cap screw as a substitute.

Head style is set by the standard: plain hex, drilled hex for safety wire, twelve point external wrenching, internal wrenching, socket head and 100 degree countersunk. Internal wrenching bolts need a heat treated countersunk NAS143C washer under the head so the large shank radius does not bear on the sharp edge of the hole, and a plain NAS143 under the nut. Close tolerance NAS bolts carry a raised or recessed triangle on the head.

Materials, finishes and the trade-offs

Pick the material for strength, temperature, corrosion and galvanic fit with the structure, then confirm the finish suits the operating temperature.

Cadmium: AC 43.13-1B says cadmium plating gives very good corrosion protection, especially in salt air, but is not recommended above 450 °F, because cadmium diffuses into the steel and makes it brittle. AN bolts are commonly cadmium plated per QQ-P-416 Type II, Class 3, which now means AMS-QQ-P-416.

Aluminum pigmented coating: NAS4006 covers aluminum coatings for fasteners, including titanium fasteners, used where galvanic corrosion against dissimilar metals or general corrosion is the concern. A coating supplier summarizes the thickness as 0.0002 to 0.0005 in, with adhesion, fluid resistance and embrittlement tests and no processing above 400 °F. Read the current edition before using those numbers for acceptance.

Passivation: stainless and A286 hardware is passivated rather than plated, normally to AMS 2700. Alloy notes are on the stainless and specialty steels and titanium alloys pages, and hot section alloys on nickel superalloys.

Torque, close tolerance fit and locking

Torque values in AC 43.13-1B Table 7-1 are derived from oil free, cadmium plated threads, so a lubricated or differently coated bolt needs its own value from the drawing or the manufacturer. Lock or safety every bolt or nut except self-locking nuts, and never reuse cotter pins or safety wire.

Close tolerance bolts are used where joints see severe load reversal and vibration. Because of the fit, they may need light tapping with a mallet to seat. The AC notes that chilling the bolt in a freezer can ease an interference fit, with the bolt allowed to warm to ambient before torquing, and it cautions against substituting for close tolerance fasteners in landing gear, control systems and rotor controls without instructions from the manufacturer or the FAA. Nut selection is covered on the nuts page and washer stacks on the washers page.

Ordering checklist

• Full part number including diameter code, material letter, drilling letters, dash number and any oversize suffix, with the standard and revision (for example NASM3 thru NASM20 rather than the cancelled AN sheet if your program requires it).
• Whether the AN part number or the NASM part number must appear on the paperwork. The numbers are identical, but some quality systems key on the document.
• Plating or coating specification and revision, such as AMS-QQ-P-416 type and class or NAS4006, plus any dry film lubricant.
• Manufacturer and lot traceability, a certificate of conformance, and material and process certs where the program requires them.
• DFARS 252.225-7009 flow down for steel, titanium and nickel alloy hardware on DoD work, and whether the commercial fastener exception may be used.
• Thread inspection requirements where UNJ to AS8879 is called.
• Packaging by lot, with no mixing of lots or manufacturers in one bag.

The RFQ checklist covers the rest of the package.

Counterfeit and quality risks, and how to receive bolts

Bolts are easy to fake because a plain hex bolt looks the same whether it was heat treated correctly or not. The main risks are commercial bolts relabeled as AN or NAS parts, wrong material or heat treatment, cadmium substitutes on parts that need cadmium, and mixed lots.

• Check head markings. AC 43.13-1B paragraph 7-36 describes AN steel bolts marked with a raised dash or asterisk, corrosion resistant steel with a single dash, aluminum alloy with two raised dashes, and close tolerance NAS bolts with a raised or recessed triangle. Special purpose bolts may be magnetic particle inspected and marked accordingly.
• Measure the grip, shank diameter and thread on a sample against the standard, and gauge UNJ threads where called.
• Match the lot number on the bag, the CoC and the manufacturer's cert.
• For DoD work, confirm the specialty metals position. DFARS 252.225-7009 exempts commercial fasteners only when the fastener manufacturer certifies that at least 50 percent of the specialty metal it buys for fasteners in the year is domestically melted or produced.

The counterfeit parts avoidance page and the receiving inspection guide go further. The DFARS specialty metals page covers the melt rules.

How we source bolts and screws

We do not stock bolts or publish prices. We buy the exact part number you specify from authorized and franchised distributors or from the manufacturer, flow down your spec revision, finish and specialty metals requirements, and check the CoC and lot paperwork before it ships. Bolts can go on the same purchase order as the machined or fabricated parts they assemble, or be packed as a kit per assembly. For superseded or hard to find numbers, we search under counterfeit avoidance controls; see obsolete aerospace parts. The wider fastener range is on the fasteners page, and permanent pin fasteners are on collars and lockbolts.

Get bolts and screws quoted with the paperwork

Send your part numbers or bill of materials with spec revisions and quantities. A person replies within one business day with one quote and one point of contact, and every order ships with a certificate of conformance. If the hardware is for a controlled program, read controlled programs first.

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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

Related

• Aerospace Nuts: Self-Locking, Castellated and Anchor Nuts
• Aerospace Washers: Flat, Countersunk, Lock, Tab and Key
• Pin and Collar Fasteners: Hi-Lok, Lockbolts and Blind Bolts
• How to Buy Obsolete Parts Without Buying Counterfeits

Sources

• FAA AC 43.13-1B, Chapter 7: aircraft hardware, nuts, washers and tables 7-12 to 7-14
• EverySpec: AN3 thru AN20 Rev. 12 Notice 1, cancelled and superseded by NASM3 thru NASM20
• DLA Troop Support: industrial hardware fastener catalog
• Standard parts hardware guide: AN bolt and anchor nut identification
• Boeing Distribution: NAS6203-26 alloy steel bolt listing
• Boeing Distribution: NAS1352 socket head cap screw listing
• SAE: AS8879 Screw Threads, UNJ Profile, Inch
• EverySpec: QQ-P-416F Notice 1, cancelled, superseded by SAE AMS-QQ-P-416
• Boeing Distribution: NAS 4006 aluminum pigmented coating
• Alumiplate: NAS 4006 compliance summary
• DFARS 252.225-7009 (JAN 2023), specialty metals, COTS and commercial fastener exceptions