When an aircraft technician opens an airframe repair manual and reaches for a rivet gun, the rivets chosen for that job are far more than fasteners — they are load-carrying structural members whose type, material, size, and installation directly determine whether the repaired structure meets its original design strength. The FAA's airframe maintenance standards, codified in Advisory Circular 43.13-1B and supported by the Aviation Maintenance Handbook (FAA-H-8083-30), treat rivet selection as a disciplined engineering process, not a casual substitution. Understanding why specific rivets belong in specific locations is foundational knowledge for any AMT preparing for the Airframe knowledge test and, more importantly, for safe, airworthy work.
This article covers the major families of solid and blind rivets used in airframe sheet-metal work, the aluminum and other alloys from which they are made, the marking systems that identify them, and the rules governing substitution and material compatibility. By the end, you should be able to look at a rivet, decode its dash numbers and head markings, and know exactly where it can and cannot be used.
Solid Shank Rivets — The Primary Structural Fastener
Solid shank rivets are the workhorses of aluminum airframe construction. They consist of a manufactured head on one end and a plain shank that is upset (bucked) on the opposite side to form a shop head. Because both the manufactured head and the shop head clamp the material, solid rivets create a very tight, permanent joint that transfers shear loads efficiently across skin panels, ribs, spars, and frames.
Alloy Designations and Head Markings
The FAA system uses a two-digit designation for rivet alloy series, and each alloy is identified by a distinctive marking (or absence of marking) on the manufactured head:
- 1100 (A) — Pure aluminum: The softest alloy; no head marking. Used only in non-structural applications such as attaching fairings, nameplates, or other non-load-bearing parts. Its low strength makes it unsuitable for primary structure.
- 2117-T4 (AD) — Dimpled dot on head: By far the most common rivet in general aviation airframes. Known as the "field rivet," 2117-T4 is used in the as-received condition — it does not require heat treatment or refrigeration before driving. Its moderate strength and excellent corrosion resistance make it the default choice for aluminum structure.
- 2017-T4 (D) — Raised tit (small raised point) on head: Stronger than 2117-T4, but must be driven within approximately one hour of removal from refrigerated storage or re-heat-treated, because it age-hardens at room temperature and becomes too brittle to drive properly. Used where higher shear strength is required.
- 2024-T4 (DD) — Two raised dashes on head: The highest-strength aluminum rivet in common airframe use. Like 2017-T4, it must be kept refrigerated until just before use and driven quickly. Reserved for highly stressed joints — heavy spar caps, wing attachment fittings — where maximum strength is essential.
- 5056 (B) — Raised cross on head: A magnesium-alloy rivet used exclusively with magnesium alloy sheet. Using an aluminum rivet in magnesium structure causes galvanic corrosion; the 5056 alloy is chosen because its electrochemical potential is close to that of magnesium.
- Monel and steel rivets: Used in steel structure and in areas subject to high heat, such as firewall attachments and exhaust regions. Monel rivets have a distinctive silver-gray color. Stainless steel rivets are used where corrosion and temperature resistance are both required.
Ice Box Rivets — Storage and Handling
Rivets made from 2017-T4 and 2024-T4 alloys are called "ice box rivets" because of the refrigeration required to keep them workable. At room temperature, the T4 temper continues to age-harden through natural precipitation hardening, and within hours the alloy becomes too hard to upset without cracking. Refrigeration (typically 0°F or below) halts this process.
The practical rule: once removed from cold storage, 2017-T4 rivets must be driven within approximately one hour and 2024-T4 within about ten to twenty minutes. If unused rivets are returned promptly to the freezer, the clock resets. Rivets that were left out too long and have hardened must be re-annealed (re-solution heat-treated) before use, or discarded. On the knowledge test, questions about ice box rivets focus on which alloys require refrigeration (2017 and 2024) and what happens if the time limit is exceeded.
Blind Rivets — When Bucking Bar Access Is Impossible
Blind rivets (also called mechanically-expanded rivets) are installed from one side only, making them essential wherever the back side of a structure is inaccessible — interior control surfaces, sealed fuel-cell bays, and complex internal structures. Several types appear in airframe work:
- Pull-type (Cherry or similar): A stem (mandrel) is pulled through the rivet body, expanding the tail on the blind side. The stem then breaks off at a predetermined load. These are available in aluminum, stainless, and Monel and are approved for structural use when specified by the manufacturer.
- Self-plugging blind rivets: The stem does not fully pull out but instead remains locked inside the rivet body, plugging the hollow shank and restoring some shear strength. These are stronger in shear than open-end pull types and are used in moderately stressed structure.
- Drive screws and specialty blind fasteners (Hi-Loks, Cherrymax): While technically beyond basic rivet categories, these engineered fasteners follow similar material and size-selection rules and are often encountered in manufacturer-specific structural repairs.
A critical point: blind rivets are generally not interchangeable with solid rivets in primary structural applications unless the manufacturer's structural repair manual (SRM) or AC 43.13-1B specifically approves the substitution. The hollow shank of most blind rivets reduces shear strength compared to an equivalent solid rivet, so size-for-size substitution is almost never valid.
Rivet Identification — AN and MS Part Numbers
Rivets are specified by AN (Army-Navy) or MS (Military Standard) part numbers that encode all the key parameters. A typical solid rivet call-out looks like this: AN470AD4-6.
- AN470 — Universal head (was formerly brazier head style); AN426 denotes a 100° countersunk (flush) head.
- AD — Alloy: 2117-T4 (as shown in the alloy table above).
- 4 — Diameter in 32nds of an inch (4/32 = 1/8 inch).
- 6 — Grip length in 16ths of an inch (6/16 = 3/8 inch grip range).
Selecting the correct grip length is critical. The rivet shank must protrude through the material by 1.5 times the rivet diameter to form a proper shop head. Too short and the shop head will be undersized and weak; too long and the shank will buckle rather than upset cleanly.
Material Compatibility and Corrosion Prevention
Galvanic corrosion is a constant concern in mixed-metal airframe repairs. The rule is straightforward: match the rivet alloy to the base material as closely as possible in electrochemical potential. For aluminum sheet (2024, 6061, 7075 series), 2117-T4 or 2024-T4 aluminum rivets are correct. For magnesium sheet, use 5056 rivets. For steel structure, use steel or Monel. Never install an aluminum rivet in a steel structure or a standard aluminum rivet through magnesium sheet.
Protective coatings also play a role. Rivets installed in areas that will be sealed or painted should be compatible with the primer and sealant system. In wet areas or marine environments, cadmium-plated steel or Monel rivets may be called for.
Key Numbers and Rules
- Minimum rivet diameter: typically 3× the thickness of the thickest sheet being joined (or per the SRM).
- Minimum edge distance: 2× rivet diameter from the center of the rivet to the nearest edge.
- Minimum pitch (rivet spacing): 3× rivet diameter center-to-center.
- Shop head dimensions: diameter approximately 1.5× shank diameter; height approximately 0.5× shank diameter.
- Ice box time limits: 2017-T4 ≈ 1 hour out; 2024-T4 ≈ 10–20 minutes out before return to storage.
- 1100 rivets: non-structural only.
- 5056 rivets: magnesium alloy structure only.
Common Test Traps
- Confusing alloy markings: The dimpled dot is 2117-T4 (AD), the raised tit is 2017-T4 (D), and the two raised dashes are 2024-T4 (DD). Students often reverse 2017 and 2117. Remember: 2117 has the extra "1" in the number and is the most common field rivet.
- Thinking blind rivets freely substitute for solid rivets: Unless the SRM or AC 43.13-1B explicitly allows it with a size upgrade, you cannot swap a blind rivet for a solid rivet of the same nominal size in primary structure.
- Ignoring ice box time limits: The test will present a scenario where a technician drives ice box rivets that were left out too long. The correct answer is that the rivets must be removed and replaced — they cannot be inspected back into service by feel or appearance alone.
- Using 1100 rivets in structural repairs: Pure aluminum (1100/A) rivets have almost no structural strength and are never appropriate for primary structure, regardless of convenience.
- Confusing AN426 with AN470: AN426 is a flush (countersunk) head rivet for aerodynamic surfaces; AN470 is a universal head. Using a universal head where a flush installation is required creates a drag-producing protrusion and may violate the SRM.