Head markings — the identification table
The mark is on the manufactured head, the one that came from the factory. Once a rivet is driven, the shop head carries no marking at all — which is why identifying rivets already in an aircraft means looking at the factory head side.
| Head marking | Code | Alloy | Storage | Typical use |
|---|---|---|---|---|
| Plain — no mark | A | 1100-F | Indefinite | Non-structural only. Fairings, trim, placards, nameplates. |
| Indented dimple | AD | 2117-T4 | Indefinite | The field rivet. The overwhelming majority of general aviation structural riveting. |
| Raised teat (single raised dot) | D | 2017-T4 | Icebox above 3/16" — see below | Higher strength than AD, where the drawing calls for it. |
| Raised double dash | DD | 2024-T4 | Icebox, all sizes — see below | Highest strength of the common aluminum rivets, and the hardest to drive. |
| Raised cross | B | 5056-H32 | Indefinite | Magnesium structures. Chosen for galvanic compatibility, not for strength. |
| Three raised dashes | — | 7075-T73 | Indefinite | High-strength aluminum rivet. AC Table 4-8 lists it as available in this head style but gives it no AN material code letter. |
Source: Table 3-1, Rivet Material Identification, US Navy Aviation Structural Mechanic training series — consistent with AC 43.13-1B and FAA-H-8083-31.
Icebox rivets — why D and DD are different
2024 (DD) rivets, and 2017 (D) rivets above 3/16 inch in diameter, are too hard to drive in their fully aged condition. They crack rather than upset. So they are solution heat treated and then kept refrigerated to suppress the natural ageing that would otherwise harden them within hours. AC 43.13-1B is precise about the threshold, and it is the part most charts get wrong: “The 2117 rivets may be driven in the condition received, but 2017 rivets above 3/16 inch in diameter and all 2024 rivets are to be kept packed in dry ice or refrigerated…” A 1/8 inch D rivet is not an icebox rivet.
Out of the freezer, the clock starts. The figure is 20 minutes at room temperature after quenching before they must be driven, or refrigerated at or below 32 °F / 0 °C. Note what refrigeration actually buys: it delays the aging time by 24 hours, not indefinitely. Exceed either limit and the rivets need re-heat-treating — you do not simply drive them harder.
2117 (AD) rivets exist precisely to avoid this. They are slightly weaker than 2017, and in exchange they need no heat treatment, no refrigeration and no clock. They can sit in a drawer for a decade and drive perfectly. This is why the great majority of what you will ever buy and drive is AD.
The practical consequence for anyone identifying rivets: if you find a raised teat or a double dash in an unlabelled drawer, you do not know its condition. It may have been out of refrigeration for years. Identifying the alloy tells you what it is; it does not tell you whether it is usable.
Head styles — AN and MS numbers
The head marking gives you the alloy. The AN or MS number gives you the head shape. Both matter, and they are different systems.
| AN number | MS equivalent | Head style | Where it is used |
|---|---|---|---|
| AN470 | MS20470 | Universal head | The general-purpose protruding head. Replaced the older round, brazier and flat heads for most new work. |
| AN426 | MS20426 | 100° countersunk (flush) | Flush surfaces — anywhere aerodynamic smoothness matters. |
| AN430 | MS20430 | Round head | Older designs, internal structure. Largely superseded by AN470. |
| AN455 | MS20455 | Brazier head | Older thin-sheet skin work. Wide, shallow head. Superseded by AN470. |
| AN442 | MS20442 | Flat head | Internal structure where clearance is tight. Superseded by AN470. |
AN and MS numbers with matching digits describe the same rivet — AN470 and MS20470 are interchangeable callouts for the universal head. MS is the later designation; you will see both in drawings depending on the vintage of the aircraft.
Reading the whole part number
Take AN470AD4-5 apart and every character earns its place:
AN470 — the head style. Universal head.
AD — the alloy code from the table above. 2117-T4.
4 — shank diameter in thirty-seconds of an inch. 4/32" = 1/8".
-5 — length in sixteenths of an inch. 5/16".
The two different fractions in one part number are not a mistake and they are the single most common misreading. Diameter is always in 32nds; length is always in 16ths. A -4 rivet is 1/4" long, not 4/32".
Where the alloy code is absent — AN470-4-5 — the drawing is specifying geometry and leaving alloy to another callout. Do not assume AD.
Worked example — identifying an unknown rivet
A rivet in an unlabelled bag, protruding head, no packaging.
- Look at the factory head under good light and at an angle. Raised features catch a shadow; indented ones fill with it.
- You see a small raised bump in the center — a raised teat. That is D, 2017-T4.
- Measure the shank with callipers: 0.125". That is 4/32", so the diameter code is 4.
- Measure the overall length under the head: 0.313". That is 5/16", so the length code is -5.
- Head shape is a universal head, so AN470.
- Full identification: AN470D4-5. And because it is a D rivet, it is an icebox rivet of unknown thermal history — identified, but not cleared for use.
AN470D4-5. Identification tells you what it is. Whether it can be driven is a separate question, and for D and DD the answer from an unlabelled bag is no.
Limits — when this chart does not settle it
A head marking is an aid to identification, not a certification.
- A marking is not traceability. Airworthy rivets come with documentation. A correctly marked rivet from an unknown source is still an unknown rivet, and identifying it does not make it installable on a certified aircraft.
- Worn, corroded and painted heads mislead. A raised teat wears down; an indented dimple fills with primer. If the mark is not unambiguous, do not guess.
- The five codes here are the aluminum rivets. Monel, CRES, titanium and 7050 have their own systems — see the note above.
- D and DD condition cannot be identified visually. Nothing about a 2024-T4 rivet's appearance tells you whether it has been out of refrigeration for twenty minutes or two years.
- Substituting alloys is a repair-design decision. AD is not a drop-in replacement for DD because it is easier to drive. The drawing specifies the alloy for a reason.
- Blind rivets are a different system entirely. CherryMAX, Olympic and similar families are identified by stem and sleeve markings under their own manufacturer schemes.
Questions people actually ask
What does AD mean on a rivet?
2117-T4 aluminum alloy, marked with an indented dimple in the center of the head. It is the standard general-purpose structural rivet in general aviation and needs no heat treatment or refrigeration.
What is the difference between AD and DD rivets?
AD is 2117-T4, marked with an indented dimple, drivable straight from the drawer. DD is 2024-T4, marked with a raised double dash, stronger, harder to drive, and an icebox rivet — it must be kept refrigerated and driven within its time limit or re-heat-treated. They are not interchangeable in either direction without approved data.
What is an icebox rivet?
A rivet that has been solution heat treated and must then be kept refrigerated to delay natural ageing. It covers all 2024 (DD) rivets and 2017 (D) rivets above 3/16 inch in diameter — smaller D rivets are not icebox rivets. Out of refrigeration they harden within about twenty minutes and will crack rather than upset cleanly.
Is MS20470 the same as AN470?
Yes. MS20470 is the later Military Standard designation for the same universal-head rivet the older AN470 callout describes. A drawing may use either depending on its vintage; the rivet is the same.
Why is there no marking on the rivets in my aircraft?
You are almost certainly looking at shop heads. The marking is on the manufactured head only, and the shop head is formed by the bucking bar with no marking at all. Find the factory-head side of the joint.
Can I identify a rivet after it is driven?
Only from the factory head, and only if it is accessible, unpainted and unworn. There is no reliable way to determine alloy from a formed shop head by eye.
Sources
- Table 3-1, Rivet Material Identification — US Navy Aviation Structural Mechanic (AS) training series — the five aluminum alloy codes, their head markings and storage requirements. Cross-checked August 2026.
- FAA AC 43.13-1B CHG 1, Chapter 4 — rivet selection, icebox rivet handling, head styles, and Table 4-8 — which alloys come in which head style, and the source of the 7075-T73 row.
- FAA-H-8083-31, AMT Handbook — Airframe, Chapter 4 — AN/MS part number anatomy and head style equivalences.
Want this as a printable?
Head markings, alloy codes, head styles and the part-number breakdown on a single page. Drawn at a size you can actually read next to a rivet.