AN Bolt Series Overview
The AN (Air Force-Navy) specification defines the standard hex bolt used across every certificated aircraft in the US fleet — from 1940s warbirds to current turboprops. Over 80 years of engineering refinement are behind this spec, which means a bolt manufactured today is directly interchangeable with one from 1943.
AN3
3/16" dia. — lightest structural bolt. Used in primary structures where weight is critical.
AN4
1/4" dia. — most common AN size. Used in the majority of airframe attachment points.
AN5
5/16" dia. — heavier loads. Wing attach, engine mount, gear attach.
AN6
3/8" dia. — heavy structural. Primary landing gear, engine mounting.
AN7
7/16" dia. — specialized. Less common than AN6 but used in heavy-duty applications.
AN8–AN20
1/2" to 1-1/4" dia. — largest AN sizes. Engine mounts, wing structures, heavy gear.
AN Bolt Identification Guide
An AN bolt is identified by a string of numbers: AN3-10A
- AN3 — Bolt series and diameter (3/16")
- 10 — Grip length in 1/16" increments (10 × 1/16" = 5/8" grip)
- A — Material/finish: A = 5% Cr steel, Cad-plated (default)
Material/finish suffix codes:
- A — 5% Cr steel, cadmium plate per QQ-P-416 Type II, Class 2
- C — A-286 alloy, 1,300°F rated — for high-temp engine applications
- D — 18-8 stainless, passivated
- F — Modified version, check spec sheet
- (No suffix) — Same as A in most cases
AN Bolt Pricing vs. OEM Distributors
We sell AN bolts sourced from Part 145-certified facilities — same MIL-SPEC material, same 8130-3 traceability, at significantly below OEM distributor pricing. The table below shows representative comparisons for the most common AN sizes.
| Part Number | Description | Aircraft Spruce (est.) | AeroSpaceSpecBolt | Stock Status |
|---|---|---|---|---|
| AN3-10A | 3/16" dia., 5/8" grip, hex | Contact for pricing | Request quote | In stock |
| AN4-10A | 1/4" dia., 5/8" grip, hex | Contact for pricing | Request quote | In stock |
| AN4-16A | 1/4" dia., 1" grip, hex | Contact for pricing | Request quote | In stock |
| AN5-10A | 5/16" dia., 5/8" grip, hex | Contact for pricing | Request quote | In stock |
| AN6-10A | 3/8" dia., 5/8" grip, hex | Contact for pricing | Request quote | In stock |
| AN8-10A | 1/2" dia., 5/8" grip, hex | Contact for pricing | Request quote | Sourcing available |
All AN bolts ship with FAA 8130-3 and Certificate of Conformance as standard. Browse our full AN bolt inventory online.
Selecting the Right Grip Length
Grip length selection is the most common point of confusion with AN bolts. The rules:
- Grip = material thickness, not total clamped range. If your material stackup is 1/2" total, use a bolt with grip ≤ 1/2".
- Use the shortest grip that fits. A shorter grip means more thread engagement in the nut.
- Count the washer stack. AN960 (flat) and AN976 (spring) washers add up. Include them in your total.
- Verify thread engagement. Minimum engagement = bolt diameter. For AN4, at least 1/4" of thread must engage the MS21042 nut.
See our full AN bolt grip length chart with torque values.
Frequently Asked Questions
AN stands for Air Force-Navy. The AN specification series was originally developed by the US Army Air Corps and Navy Bureau of Aeronautics during WWII as a unified standard for aircraft hardware. The AN designation covers bolts, nuts, washers, and pins used in airframe construction and maintenance.
The grip length is the thickness of the material being clamped — not including the bolt head or nut. AN bolts are available in grip lengths from 1/8" to several inches. The final grip is calculated as bolt thread length minus the nut and washer stackup. See our grip length guide for detailed selection tables.
Standard AN bolts are manufactured from corrosion-resistant steel (CRES) per QQ-P-416 or equivalent. The most common is 5% chrome steel or 18-8 stainless. Material is identified on the part and in the MIL-SPEC. High-temperature applications may use A-286 or other superalloys.
AN hex bolts are typically rated at 125,000 psi tensile strength (AN-STD-20, Type 1). Specific AN bolts may be rated differently — check the applicable MS or AN specification sheet. The bolt markings on the head indicate material and classification.
Standard AN bolts can be used in composite structures with proper attention to hole sizing and torque values. CRES bolts are preferred over cadmium-plated steel in composite applications to avoid galvanic corrosion. Specific composite attachment hardware may have different specifications.
Search our full AN bolt inventory
Browse every AN3–AN20 SKU in stock with pricing, lead times, and cert availability. For bulk orders, submit an RFQ and get a response within 1 business day.