In aerospace engineering, precision, safety, and reliability are absolutely critical. Every component, even the smallest fastener, directly impacts aircraft performance and operational safety. Fasteners—such as bolts, screws, rivets, and nuts—must meet strict specifications to endure vibration, thermal expansion, and extreme aerodynamic and structural loads during flight.
This Aerospace Fastener Size Guide provides detailed guidance on selecting the right fasteners, including materials, sizing charts, and industry standards.
What Are Aerospace Fasteners?
Aerospace fasteners are specialized mechanical components engineered to secure aircraft structures and systems. Unlike standard industrial fasteners, they are designed to endure extreme conditions, including high stress, temperature fluctuations, corrosion, and fatigue from repeated vibration.
Common types include bolts, screws, nuts, rivets, and washers, each selected carefully to ensure safety, reliability, and long-term structural integrity in demanding aerospace applications.
High stress
Extreme temperatures
Corrosion
Fatigue from repeated vibration
Common aerospace fasteners include bolts, screws, nuts, rivets, and washers.
Why Proper Fastener Sizing Matters
Selecting the correct fastener size and type is critical in aerospace applications. Using an incorrect fastener can weaken structural integrity, cause premature component failure, and compromise flight safety.
Proper fastener sizing ensures that aircraft structures remain secure, vibrations are managed, loads are supported effectively, and all components comply with strict aviation standards and regulatory requirements.
1-Aircraft Structural Integrity
Correctly sized fasteners are essential for maintaining the structural integrity of an aircraft. They securely join components, distributing loads evenly to prevent stress concentrations or deformation. Ensuring proper fastener engagement and torque helps the airframe withstand aerodynamic forces, thermal expansion, and operational stresses, keeping the aircraft safe and structurally sound throughout its service life.
2-Vibration Resistance
Aerospace fasteners must resist vibration from engines, turbulence, and operational maneuvers. Properly sized fasteners prevent loosening or fatigue failure under repeated vibrational loads. Using the correct type and size ensures secure connections, minimizes micro-movements between components, and maintains consistent performance, reducing the risk of structural damage or in-flight failures caused by vibration-induced loosening.
3-Load-Bearing Capability
Fasteners in aerospace applications must support both static and dynamic loads without deforming or failing. Choosing the right size and strength ensures that each fastener can handle operational stresses safely. Proper sizing allows the load to be distributed across multiple fasteners, preventing overstressing individual components and maintaining the overall structural reliability of the aircraft.
4-Compliance with Aviation Regulations
Aerospace fasteners must meet strict industry standards and regulatory requirements to ensure safety and airworthiness. Proper sizing and material selection ensure compliance with aviation codes such as FAA, EASA, or military specifications. Using approved fasteners reduces liability, ensures certification standards are met, and maintains the aircraft’s operational safety throughout its lifecycle.
Common Types of Aerospace Fasteners
Aerospace fasteners come in a variety of types, each designed for specific applications and performance requirements. Understanding the functions and characteristics of bolts, screws, nuts, rivets, and washers is essential for proper selection. Choosing the right fastener type ensures structural integrity, vibration resistance, load distribution, and long-term reliability in demanding aerospace environments.
1 Bolts
Bolts are widely used to securely join two or more components and are typically paired with compatible nuts. They provide strong, removable connections capable of withstanding high loads and vibrations. Aerospace bolts are precisely engineered to meet strict material and dimensional standards, ensuring reliable performance in critical airframe and system assemblies under extreme operational conditions.
2 Screws
Screws are self-threading fasteners ideal for securing lightweight panels, interior components, and assemblies where removable connections are needed. They can be installed without nuts and are commonly used in areas where space is limited. Proper selection of screw type, length, and material ensures mechanical strength, vibration resistance, and long-term durability.
3 Nuts
Nuts complement bolts and screws by providing secure, threaded connections. Aerospace nuts often incorporate locking mechanisms, such as prevailing torque or nylon inserts, to resist loosening under vibration and thermal cycling. Selecting the correct nut type and size is crucial for maintaining joint integrity and ensuring the fastener assembly performs safely under high-stress and dynamic flight conditions.
4 Rivets
Rivets are permanent fasteners commonly used in fuselage skins, wing structures, and other load-bearing components. They provide strong, vibration-resistant joints that cannot be easily disassembled. Aerospace rivets come in various types, including solid, blind, and structural rivets, each chosen based on material, load requirements, and accessibility during assembly or repair.
5 Washers
Washers are thin plates placed under bolt or screw heads and nuts to distribute loads, prevent loosening, and protect materials from damage. In aerospace applications, washers help maintain joint integrity, reduce stress concentrations, and enhance vibration resistance. Selecting the appropriate washer type, size, and material ensures reliable performance and extends the service life of the fastened assembly.
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Aerospace Fastener Materials
Aerospace fasteners must be made from materials that can withstand corrosion, fatigue, and high temperatures while maintaining strength and reliability. Common materials include stainless steel, titanium alloys, aluminum alloys, and nickel-based alloys.
Selecting the appropriate material is critical, as it affects fastener strength, weight, and compatibility with surrounding aircraft components and structural materials.
Stainless Steel (304, 316, 17-4 PH)
Titanium Alloys (Grade 5, Grade 23)
Aluminum Alloys (2024, 7075)
Nickel-based alloys
Material selection affects strength, weight, and compatibility with aircraft materials.
Fastener Standards and Specifications
Aerospace fasteners must meet strict industry standards to ensure safety, reliability, and compatibility. Common standards include NAS (National Aerospace Standard), MS (Military Standard), AS (Aerospace Standard), and DIN/ISO for metric fasteners.
These specifications govern dimensions, material grades, torque ratings, and testing procedures, ensuring that fasteners perform consistently under the extreme conditions encountered in aerospace applications.
NAS (National Aerospace Standard)
MS (Military Standard)
AS (Aerospace Standard)
DIN / ISO for metric fasteners
These standards define dimensions, material grades, torque requirements, and testing procedures.
Understand Fastener Size Terminology
Accurate fastener sizing in aerospace applications requires familiarity with key terminology. Understanding terms such as diameter, length, thread pitch, grip length, and head type is essential for selecting fasteners that fit properly, distribute loads correctly, and perform reliably under vibration, stress, and extreme environmental conditions. Proper interpretation of these terms ensures safety and structural integrity.
1-Diameter
The diameter of a fastener refers to the nominal width of its shaft. In aerospace applications, precise diameter selection is critical to ensure a proper fit in the mating components, maintain load-bearing capacity, and prevent loosening under vibration or stress. Diameter affects torque requirements, strength, and compatibility with corresponding nuts, washers, or threaded holes.
2-Length
Length is the total measurement of a fastener from the head to the tip of the shaft. Selecting the correct length ensures full engagement of threads or rivet shanks without excess protrusion, maintaining structural integrity and proper load distribution. Accurate length selection also prevents interference with other components and allows for proper torque application.
3-Thread Pitch
Thread pitch is the distance between adjacent threads on a bolt or screw. Proper thread pitch ensures smooth engagement with nuts or threaded holes, maintains correct torque application, and distributes load evenly. Using the correct thread pitch is essential to prevent stripping, loosening, or fatigue failure in aerospace assemblies subjected to vibration and dynamic loads.
4-Grip Length
Grip length is the portion of a bolt or screw that is fully engaged in the material, excluding threads extending beyond the connection. Correct grip length ensures the fastener holds components securely, distributes clamping force effectively, and prevents over-compression or joint separation. Accurate grip length is critical for load-bearing and vibration-resistant aerospace applications.
5-Head Type
The head type refers to the shape and style of the fastener’s head, such as countersunk, pan, hex, or button head. Choosing the proper head type affects load distribution, flush mounting, torque application, and access for tools. Correct head selection ensures reliable fastening, reduces stress concentrations, and maintains aerodynamic or structural requirements in aerospace assemblies.
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Determining Fastener Size for Aerospace Applications
Selecting the correct fastener size in aerospace applications involves careful consideration of multiple factors. Key considerations include material thickness, load requirements, environmental conditions, and exposure to vibration and fatigue. The general guideline is to choose the smallest diameter fastener that safely supports the load, minimizing weight while ensuring structural integrity and reliable, long-term performance.
1-Material Thickness
When selecting aerospace fasteners, the thickness of the material being joined is critical. The fastener must fully engage the material to provide adequate clamping force without causing deformation or damage. Choosing the correct length and grip ensures proper load distribution, prevents joint separation, and maintains structural integrity under operational stresses, vibration, and thermal expansion.
2-Load Requirements
Fasteners must be sized to handle the static and dynamic loads they will encounter during flight. This includes both tensile and shear forces. Selecting a fastener that meets or exceeds the required load ensures the joint remains secure under stress, prevents fatigue failure, and maintains overall aircraft safety, especially in high-stress or critical structural areas.
3-Environmental Conditions
Environmental factors such as temperature extremes, humidity, and exposure to corrosive agents affect fastener performance. Aerospace fasteners must be made from materials and coatings that resist corrosion, thermal expansion, and chemical degradation. Correct sizing combined with suitable material selection ensures long-term reliability, prevents joint failure, and maintains structural integrity in harsh operational environments.
4-Vibration and Fatigue Considerations
Aerospace fasteners are exposed to repeated vibration and cyclical loading, which can lead to fatigue failure over time. Proper fastener sizing, combined with appropriate locking mechanisms and material choice, helps resist loosening and cracking. Accounting for vibration and fatigue ensures secure connections, extends service life, and maintains safety during repeated operational cycles and high-stress maneuvers.
5-General Sizing Rule
The general principle for aerospace fastener selection is to choose the smallest diameter that safely supports the load. Smaller fasteners reduce weight without compromising strength or structural integrity. Proper sizing balances efficiency, performance, and reliability, ensuring that joints are secure, vibration-resistant, and able to withstand operational stresses over the aircraft’s service life.
The general rule is: select the smallest diameter fastener that safely supports the load to reduce weight while maintaining structural integrity.
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Bolts and Screws Size Chart
This table provides a reference for common aerospace bolt and screw sizes, including diameter, length, thread pitch, material, and typical applications. It helps engineers select the appropriate fasteners for specific components, from instrument panels to engine mounts, ensuring proper fit, strength, and compliance with aerospace standards while maintaining structural integrity and reliability.
| Diameter (in) | Length (in) | Thread Pitch | Material | Typical Application |
|---|---|---|---|---|
| 1/4 | 1 – 2 | 20 TPI | Titanium | Instrument panels |
| 5/16 | 1 – 3 | 18 TPI | Stainless Steel | Wing attachments |
| 3/8 | 1 – 4 | 16 TPI | Aluminum | Interior assemblies |
| 1/2 | 2 – 6 | 13 TPI | Titanium | Landing gear brackets |
| 5/8 | 3 – 8 | 11 TPI | Nickel Alloy | Engine mounts |
Rivet Sizing Guide
Rivets are sized based on diameter and grip range to ensure adequate shear strength and fatigue resistance in aerospace applications. Proper selection prevents joint failure and maintains structural integrity. Diameters typically range from 3/32 inch to 1/2 inch, while the grip range corresponds to the combined thickness of the materials being clamped, ensuring a secure, reliable connection.
Diameter: Typically 3/32 in to 1/2 in
Grip Range: Material thickness that the rivet can clamp
Rivet Size Chart
This table provides a reference for common aerospace rivet types, including diameter, grip range, material, and typical applications. It helps engineers select the right rivet for specific uses, from fuselage skins to wing structures and interior panels. Proper rivet sizing ensures adequate shear strength, fatigue resistance, and long-term structural integrity in demanding aerospace environments.
| Rivet Type | Diameter (in) | Grip Range (in) | Material | Typical Use |
|---|---|---|---|---|
| Solid Rivet | 3/32 – 3/16 | 0.030 – 0.125 | Aluminum | Fuselage skin |
| Blind Rivet | 1/8 – 1/4 | 0.062 – 0.250 | Stainless Steel | Panels, interiors |
| Cherry Rivet | 3/16 – 1/4 | 0.125 – 0.250 | Aluminum | Wing skins |
| Hi-Lok Rivet | 1/8 – 1/4 | 0.062 – 0.250 | Titanium | Critical structures |
Torque Requirements and Load Considerations
Aerospace fasteners must be tightened to precise torque values to achieve proper clamping without overstressing components or compromising joint integrity. Torque is calculated using the formula: T = k × D × F, where T is torque, k is the torque coefficient, D is the fastener diameter, and F is the clamping force. Manufacturer torque charts ensure safe, consistent, and repeatable assembly.
Torque Formula (in-lb or N·m):
T = k × D × F
Where:
T = Torque
k = Torque coefficient (depends on lubrication)
D = Diameter
F = Clamping force
Torque charts provided by manufacturers ensure safe and repeatable assembly.
Nut and Washer Sizing
Nuts and washers must be compatible with the fastener’s diameter, thread, and material. In high-vibration environments, locking nuts—such as self-locking or prevailing torque types—are used to prevent loosening. Proper selection ensures secure connections, even under dynamic loads, and protects the integrity and reliability of aerospace assemblies.
Nut and Washer Size Chart
This table provides a reference for selecting nuts and washers that match specific fastener diameters in aerospace applications. It includes nut types, compatible washer types, and recommended materials. Proper selection ensures secure, vibration-resistant joints and maintains structural integrity, helping fasteners perform reliably under the extreme loads and environmental conditions encountered in aircraft assemblies.
| Fastener Diameter | Nut Type | Washer Type | Material |
|---|---|---|---|
| 1/4 | MS21047 | Flat, Lock | Stainless Steel |
| 5/16 | MS21048 | Flat, Lock | Titanium |
| 3/8 | MS21049 | Flat, Lock | Aluminum |
| 1/2 | MS21050 | Flat, Lock | Nickel Alloy |
| 5/8 | MS21051 | Flat, Lock | Stainless Steel |
Environmental Factors in Fastener Selection
Aerospace fasteners must withstand harsh environmental conditions to ensure long-term reliability and safety. They are exposed to saltwater, fuel, hydraulic fluids, and extreme temperatures ranging from -65°C to 150°C. Protective coatings—such as cadmium plating, anodizing, or PTFE—are commonly applied to prevent corrosion, reduce wear, and maintain structural integrity in demanding aerospace environments.
Saltwater (marine environments)
Fuel and hydraulic fluids
Extreme temperatures (-65°C to 150°C)
Coatings such as cadmium plating, anodizing, or PTFE are common in aerospace fasteners.
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Aerospace Fastener Weight Considerations
Minimizing fastener weight is crucial for overall aircraft efficiency and fuel economy. Lightweight materials like titanium and aluminum are preferred in areas where reducing mass is critical, while stronger materials such as steel and nickel alloys are chosen for high-load or structural applications. Balancing weight and strength ensures both performance and safety in aerospace assemblies.
Fastener Selection Checklist
When selecting aerospace fasteners, follow a systematic approach to ensure safety and reliability: identify load and application requirements, determine material compatibility, select the appropriate diameter and length, verify rivet grip range, ensure torque specifications are achievable, check compliance with NAS/MS/AS standards, consider environmental conditions, and evaluate weight requirements for optimal performance.
Identify load and application requirements
Determine material compatibility
Select diameter and length
Verify grip range for rivets
Ensure torque specifications are achievable
Check compliance with NAS/MS/AS standards
Consider environmental conditions
Evaluate weight requirements
Aerospace Fastener Application Examples
Different aerospace components require specific fasteners based on load, material, and environment: fuselage assemblies use solid aluminum rivets ranging from 3/32 to 1/4 inch; wing mounts often employ high-strength titanium bolts of 5/16 to 1/2 inch; engine mount brackets use nickel alloy bolts from 1/2 to 5/8 inch; and cabin interiors rely on stainless steel screws and nuts between 1/4 and 3/8 inch.
Fuselage assembly: Solid rivets, aluminum, 3/32 in – 1/4 in diameter
Wing mounting: High-strength bolts, titanium, 5/16 – 1/2 in diameter
Engine mount brackets: Nickel alloy bolts, 1/2 – 5/8 in diameter
Cabin interiors: Stainless steel screws and nuts, 1/4 – 3/8 in diameter
Common Aerospace Fastener Mistakes
Frequent fastener errors can compromise aircraft safety and performance. Common mistakes include using the wrong diameter or length, ignoring torque specifications, selecting incompatible materials, overlooking vibration-resistant locking requirements, and neglecting corrosion protection. Avoiding these errors ensures secure, reliable assemblies, enhances structural integrity, improves safety, and reduces maintenance and repair costs over the aircraft’s service life.
Using incorrect diameter or length
Ignoring torque specifications
Using incompatible materials
Overlooking vibration locking requirements
Ignoring corrosion resistance
Avoiding these mistakes improves aircraft safety and reduces maintenance costs.
Advanced Fastener Sizing Tools
Modern aerospace engineers rely on advanced tools to accurately size fasteners and ensure reliable assemblies. CAD software with integrated fastener libraries, Finite Element Analysis (FEA) for simulating loads, and manufacturer torque and size charts help optimize selection. Using these tools minimizes trial-and-error, enhances structural integrity, and ensures safe, efficient, and repeatable fastener installation.
CAD software with built-in fastener libraries
FEA (Finite Element Analysis) for load simulations
Manufacturer torque and size charts
These tools reduce trial-and-error and improve assembly reliability.
Industry Standards Quick Reference
This table provides a quick reference for common aerospace fastener standards, including NAS, MS, AS, and ISO/DIN. It lists applicable fastener types, typical materials, and common uses. Following these standards ensures that fasteners meet strict dimensional, material, and performance requirements, maintaining safety, reliability, and compliance in both critical and non-critical aerospace assemblies.
| Standard | Fastener Type | Material | Typical Use |
|---|---|---|---|
| NAS (National Aerospace Standard) | Bolt, Screw, Nut | Titanium, Stainless Steel | Aircraft structures |
| MS (Military Standard) | Rivet, Bolt, Nut | Aluminum, Steel | Fuselage, wing assembly |
| AS (Aerospace Standard) | Bolt, Screw | Titanium | Critical structures |
| ISO/DIN | Bolt, Nut | Stainless Steel | Non-critical components |
Final Thoughts
Selecting the correct aerospace fastener involves careful evaluation of size, material, load capacity, environmental factors, and compliance with industry standards. A structured selection process ensures safety, reliability, and weight efficiency. By following this Aerospace Fastener Size Guide, engineers can confidently choose fasteners that meet performance requirements and maintain structural integrity across all aircraft applications.
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FAQs:
What is the standard aircraft bolt?
The standard aircraft bolt is the AN (Army-Navy) bolt, commonly used in aerospace applications. AN bolts are manufactured from high-strength alloy steel or corrosion-resistant materials and follow strict military standards for size, strength, and thread accuracy to ensure safety, reliability, and interchangeability in aircraft structures.
What size is an AN2 bolt?
An AN2 bolt has a nominal diameter of 1/8 inch. The length of the bolt is indicated by the dash number following AN2, measured in eighths of an inch. For example, an AN2-5 bolt is 5/8 inch long, excluding the bolt head.
What is the standard size of bolts?
There is no single standard bolt size, as sizes vary by application and industry. Bolts are generally classified by diameter, length, and thread type. In aerospace, common standards include AN, MS, and NAS bolts, which follow precise sizing systems designed for strength, weight, and performance requirements.
What size are aircraft screws?
Aircraft screws range in size depending on their purpose, but common diameters include #4, #6, #8, and #10. Lengths vary based on installation needs. Aerospace screws are made to AN, MS, or NAS standards and are designed to withstand vibration, load stress, and extreme environmental conditions.
What are the three types of bolts?
The three main types of bolts are machine bolts, structural bolts, and special-purpose bolts. Machine bolts are used for general fastening, structural bolts handle high loads, and special-purpose bolts are designed for specific applications such as aerospace, automotive, or heavy-duty industrial use.
How are aircraft bolts measured?
Aircraft bolts are measured by diameter and length. The diameter is identified by the AN or NAS number, while the length is measured from the underside of the bolt head to the end of the shank. Lengths are typically indicated in eighths of an inch using dash numbers.