Hex bolt dimensions vary by size and standard. Inch series bolts range from 1/4″ to 2″ in diameter, with head widths from 7/16″ to 3-1/8″. Metric bolts range from M4 to M64, with head widths from 7mm to 95mm. Thread lengths depend on diameter and length.
Hex Bolt Dimensions
| Size | WAF S | Head Height K | Thread Length B | ||||
| Min | Max | Min | Max | ≥ 125 | > 125 ≥ 200 | ≥ 200 | |
| M2 | 3.82 | 4.00 | 1.28 | 1.52 | 10 | – | – |
| M3 | 5.32 | 5.50 | 1.88 | 2.12 | 12 | – | – |
| M4 | 6.78 | 7.00 | 2.68 | 2.92 | 14 | – | – |
| M5 | 7.78 | 8.00 | 3.35 | 3.65 | 16 | 22 | – |
| M6 | 9.78 | 10.00 | 3.85 | 4.15 | 18 | 24 | – |
| M8 | 12.73 | 13.00 | 5.15 | 5.45 | 22 | 28 | 41 |
| M10 | 16.73 | 17.00 | 6.22 | 6.58 | 26 | 32 | 45 |
| M12 | 18.67 | 19.00 | 7.32 | 7.68 | 30 | 36 | 49 |
| M14 | 21.67 | 22.00 | 8.62 | 8.98 | 34 | 40 | 53 |
| M16 | 23.67 | 24.00 | 9.82 | 10.2 | 38 | 44 | 57 |
| M18 | 26.67 | 27.00 | 11.28 | 11.7 | 42 | 48 | 61 |
| M20 | 29.67 | 30.00 | 12.28 | 12.7 | 46 | 52 | 65 |
| M22 | 31.61 | 32.00 | 13.78 | 14.2 | 50 | 56 | 69 |
| M24 | 35.38 | 36.00 | 14.78 | 15.2 | 54 | 60 | 73 |
| M27 | 40.00 | 41.00 | 16.65 | 17.4 | 60 | 66 | 79 |
| M30 | 45.00 | 46.00 | 18.28 | 19.12 | 66 | 72 | 85 |
| M33 | 49.00 | 50.00 | 20.58 | 21.42 | 72 | 78 | 91 |
| M36 | 53.80 | 55.00 | 22.08 | 22.92 | 78 | 84 | 97 |
| M39 | 58.80 | 60.00 | 24.58 | 25.42 | 84 | 90 | 103 |
| M42 | 63.10 | 65.00 | 25.58 | 26.42 | 90 | 96 | 109 |
| M45 | 68.10 | 70.00 | 27.58 | 28.42 | 96 | 102 | 115 |
| M48 | 73.10 | 75.00 | 29.58 | 30.42 | 102 | 108 | 121 |
| M52 | 78.10 | 80.00 | 32.5 | 33.5 | – | 116 | 129 |
| M56 | 82.80 | 85.00 | 34.5 | 35.5 | – | 124 | 137 |
| M60 | 87.80 | 90.00 | 37.5 | 38.5 | – | 132 | 145 |
| M64 | 92.80 | 95.00 | 39.5 | 40.5 | – | 140 | 153 |
What Are Hex Bolts?
A hex bolt, also known as a hex cap screw, is a threaded fastener with a six-sided head, allowing for easy gripping and precise torque application. It provides strong, reliable connections in structural and mechanical applications.
However, selecting the right hex bolt involves trade-offs. Larger bolts offer greater strength but require more space and heavier tools for installation. Meanwhile, finer thread pitches provide better grip but take longer to fasten.
Choosing the right dimensions impacts performance, durability, and assembly efficiency. Understanding these factors ensures secure, long-lasting connections while balancing cost, material constraints, and ease of use.
Standard Hex Bolt Dimensions and Specifications
Hex bolts come in a variety of sizes, each with standardized measurements for diameter, length, and thread pitch to ensure compatibility across applications. Selecting the right dimensions is crucial for strength, ease of installation, and performance.
Larger bolts handle greater loads but require more space and heavier tools. Finer threads provide better grip but can be harder to install, while coarser threads resist stripping and are easier to work with. Balancing these factors ensures secure, cost-effective, and efficient fastening solutions.
Diameter and Thread Pitch
The diameter of a hex bolt is measured across the external threads, while the thread pitch refers to the distance between adjacent threads. Larger diameters enhance shear strength, making bolts more resistant to heavy loads, but they also require bigger holes and tools.
Fine-threaded bolts create stronger clamping forces and are ideal for precision applications. However, they are prone to stripping and require careful handling.
Coarse-threaded bolts, on the other hand, install faster and are more resistant to dirt and damage, making them preferable for heavy-duty and outdoor applications. Choosing the right combination depends on load requirements and environmental factors.
Bolt Length Measurement
The length of a hex bolt is measured from the understand bearing surface to the end, excluding the head. Longer bolts provide deeper engagement, increasing joint strength.
However, using an overly long bolt can lead to wasted material, excess weight, and installation difficulties. Shorter bolts may not engage threads fully, compromising holding power. Proper selection ensures secure fastening without unnecessary material waste.
Head Size and Wrench Compatibility
Hex bolt head sizes vary based on diameter, and using the correct wrench size is essential for proper torque application. Larger heads allow for higher torque but need more space.
Smaller heads fit tight spaces but may limit applied force. Selecting the right head size ensures secure installation and prevents stripping or overtightening.
Metric vs. Imperial Hex Bolt Sizes
Hex bolts are manufactured in both metric and imperial (inch) measurements, with different global standards. Metric bolts use millimeter-based sizing, while imperial bolts are measured in fractions of an inch. Choosing the right system impacts wrench compatibility, thread matching, and overall project efficiency.
Interchangeability is a challenge since metric and imperial threads rarely align, leading to stripped threads or misalignment. Availability also varies; metric bolts dominate internationally, while imperial fasteners remain common in the U.S. Precision is another factor—metric bolts offer finer size increments, while imperial bolts provide coarser steps, which can be more forgiving.
Selecting the right system depends on industry standards, equipment compatibility, and long-term maintenance needs. Understanding these trade-offs ensures efficient assembly, reduces errors, and enhances structural integrity in any application.
Common Materials and Grades of Hex Bolts
Hex bolts are available in various materials and grades, each offering different levels of strength, corrosion resistance, and suitability for specific applications.
Selecting the right material involves balancing factors like durability, cost, and environmental conditions. While stronger bolts provide better load capacity, they may be more brittle or expensive.
Conversely, corrosion-resistant materials extend the bolt’s lifespan but may lack the necessary strength for heavy-duty uses. Understanding these trade-offs is essential for choosing the best hex bolt for your project.
Steel Grades and Strength Ratings
Hex bolts made from steel are classified by grade numbers, such as Grade 2, Grade 5, and Grade 8, which indicate their strength and hardness. Grade 2 bolts are the most affordable but are best suited for light-duty applications where extreme strength isn’t required.
Grade 5 bolts, commonly used in construction and automotive industries, offer better strength and moderate toughness, making them a versatile option. Grade 8 bolts are the strongest of the three, designed for heavy machinery and high-stress environments.
However, higher-strength bolts can be more brittle and require careful handling to prevent breakage. Choosing the appropriate steel grade involves balancing the need for strength against cost and the demands of the application.
Stainless Steel and Corrosion Resistance
Stainless steel hex bolts are ideal for applications where corrosion resistance is a priority, such as marine, chemical, or outdoor environments. Unlike carbon steel, stainless steel resists rust and oxidation, making it perfect for exposure to moisture.
However, these bolts are generally softer than high-grade steel bolts, limiting their strength. They are also more expensive, making them less practical for heavy-load applications where corrosion resistance is not a primary concern.
Other Materials: Brass, Titanium, and More
In addition to steel and stainless steel, hex bolts are available in specialized materials like brass and titanium. Brass offers excellent corrosion resistance and is non-magnetic, but it is softer and unsuitable for heavy loads. Titanium, while lightweight and corrosion-resistant, is costly and typically used in aerospace and medical industries.
Choosing the Right Hex Bolt for Your Application
Selecting the correct hex bolt requires careful consideration of factors such as load-bearing capacity, environmental conditions, and industry standards. Start by assessing the strength needed for your application.
While larger bolts provide more strength, they demand more space and higher costs. For lighter loads, smaller bolts may be sufficient, though they risk failure under stress. Environmental conditions are also crucial.
If exposed to moisture or chemicals, corrosion-resistant materials like stainless steel or coated bolts are necessary to ensure longevity. However, they can be more expensive and may not offer the same strength as carbon steel bolts. On the other hand, steel bolts can handle heavier loads but may require protective coatings for outdoor use.
Balancing these trade-offs is essential. Industry standards also play a role, as certain sectors require specific bolt specifications. By considering all factors, you can choose the ideal hex bolt for your project’s needs.
How to Read Hex Bolt Specifications on a Drawing or Label
Understanding the markings and specifications on hex bolt packaging or engineering drawings ensures you select the right fastener for your needs. Typically, the specifications include key details such as bolt diameter, length, thread pitch, and material grade. For example, a bolt marked as “M10x1.5” indicates a metric bolt with a 10mm diameter and a 1.5mm thread pitch.
Additionally, strength and material grade information is crucial. Hex bolts might be marked with a grade, such as “Grade 5” or “A2-70” for stainless steel. These grades indicate the bolt’s tensile strength and hardness, affecting its load capacity and resistance to stress. Higher-grade bolts are stronger but may cost more or be more brittle.
Interpreting these specifications helps balance performance and cost. Always ensure you choose bolts that meet both technical and environmental requirements, as improper selection could lead to failure or unnecessary expenses.
Conclusion
Hex bolts are essential fasteners with standardized dimensions, making them ideal for a variety of applications in construction, machinery, and industrial settings. Choosing the right bolt involves balancing factors like strength, material, and environmental conditions. By considering these trade-offs, you ensure the optimal performance and durability of your assembly.
FAQs
1. What is the difference between hex bolts and hex cap screws?
Hex bolts and hex cap screws are similar, but hex bolts have a flat end, while hex cap screws have a fully threaded shaft and a rounded head. Hex bolts are generally used for through holes, while cap screws are used for precision applications requiring a tighter fit.
2. How do I know which grade of hex bolt to choose?
The grade of a hex bolt indicates its strength and hardness. For general use, Grade 5 bolts are often sufficient, while Grade 8 is used for heavy-duty applications. Stainless steel bolts offer corrosion resistance but may be softer than steel bolts, so choosing the right grade depends on the specific strength and durability needed.
3. What does the thread pitch of a hex bolt mean?
Thread pitch refers to the distance between adjacent threads on the bolt. A finer thread pitch provides better grip, making it ideal for precise applications, while a coarser pitch is easier to install and resists damage in softer materials. Choosing the right pitch ensures better performance based on load and material.
4. Can I use a hex bolt in any application?
No, hex bolts are not one-size-fits-all. It’s crucial to consider the application’s load requirements, environmental conditions (like exposure to moisture or chemicals), and the material of the bolt. For outdoor or marine environments, corrosion-resistant materials such as stainless steel are preferable, while steel bolts are suitable for heavy-duty use in dry environments.
5. How do I read the specifications on a hex bolt label?
Hex bolt labels typically include the diameter, thread pitch, material grade, and length. For example, an “M10x1.5” bolt indicates a 10mm diameter with a 1.5mm thread pitch. Strength grades like “Grade 5” or “A2-70” provide additional information on the bolt’s strength and material, helping you choose the right bolt for your project.