Bolt Grade Markings & Strength Chart (M6-M20)
Trust CNRL for reliable automotive fasteners. Our complete guide covers bolt grades, thread pitch, strength, sizes, and torque for metric and imperial bolts, helping distributors and wholesalers select the right products for their projects.
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What is Bolt Grades and Markings
Understanding bolt grade markings and their corresponding strength is essential for any project’s safety and performance. The grade of a bolt indicates its tensile and yield strength, crucial for automotive, construction, and mechanical applications.
As a leading automotive fastener manufacturer, CNRL operates a modern factory with over 120 employees, producing bolts from grade 4.8 to 12.9, with diameters ranging from 3mm to 30mm and lengths from 6mm to 300mm. We have stable partnerships with top-tier brands like ZF, TENNECOF, and FAW, ensuring safe and efficient products for your projects.
Bolt Grade & Strength Chart
To select the correct fastener for your application, you must understand the strength properties of each grade. Below are the key specifications for both metric and imperial bolts.
| Bolt Grade | Tensile Strength (MPa) | Yield Strength (MPa) | Recommended Torque Range (Nm) |
|---|---|---|---|
| 4.8 | 400 | 320 | 11.8 – 57.3 |
| 5.6 | 500 | 300 | 13.3 – 64.1 |
| 8.8 | 800 | 640 | 32.3 – 143 |
| 10.9 | 1040 | 940 | 59 – 167 |
| 12.9 | 1220 | 1100 | 95.7 – 277 |
Note:
Recommended torque ranges are based on standard values for bolt diameters M6 to M20 and may vary depending on actual specifications and application conditions, please contact CNRL’s expert team for verification.
| Bolt Grade | Tensile Strength (PSI) | Yield Strength (PSI) | Recommended Torque Range (lb-ft) | Notes |
|---|---|---|---|---|
| SAE Grade 2 | 74,000 | 55,000 | 7 – 120 | Low/medium strength, general-purpose bolts |
| SAE Grade 5 | 120,000 | 85,000 | 12 – 185 | Medium strength, commonly used in automotive and machinery |
| SAE Grade 8 | 150,000 | 130,000 | 20 – 300 | High strength, heavy-duty applications |
| UNC Threads | / | / | Depends on bolt size | Unified Coarse Thread, standard for most bolts |
| UNF Threads | / | / | Depends on bolt size | Unified Fine Thread, tighter fit and higher tensile capacity |
Notes:
⚫️Torque ranges depend on bolt diameter, lubrication, and application.
⚫️UNC/UNF threads ensure compatibility and strength for imperial systems.
⚫️Values are based on SAE J429 standard and verified sources.
Need expert guidance?
Beyond standard grades, special materials offer enhanced strength and corrosion resistance. We supply a variety of options, including:
⚫️Stainless Steel (A2-70 / A4-80): Provides excellent corrosion resistance with high tensile strength.
⚫️Titanium Alloy: Lightweight and extremely strong, ideal for performance-critical applications.
⚫️Alloy Steel: Heat-treated for exceptional strength and durability.
Bolt Size & Thread Reference Chart
Choosing the right bolt size and thread pitch is crucial for a secure fit. Use these charts as a quick reference for common dimensions and compatibility.
Metric Bolt Size Chart
Notes:
⚫️Hex head size is measured across flats (AF) for standard DIN/ISO hex bolts.
⚫️Typical lengths represent commonly stocked sizes; custom lengths are available.
⚫️Standard pitch follows ISO 261/262 metric coarse thread standard.
Unsure which bolts fit your project?
| Bolt Size | Standard Pitch (mm) | Recommended Hex Head Size (mm) | Typical Lengths (mm) | Notes |
|---|---|---|---|---|
| M3 | 0.5 | 5.5 | 6, 8, 10, 12, 16, 20 | Small machine screws, light-duty fastening |
| M4 | 0.7 | 7 | 8, 10, 12, 16, 20, 25 | Common for electronics and machinery |
| M5 | 0.8 | 8 | 10, 12, 16, 20, 25, 30 | Medium-duty applications |
| M6 | 1.0 | 10 | 12, 16, 20, 25, 30, 40 | Automotive, machinery, general fastening |
| M8 | 1.25 | 13 | 16, 20, 25, 30, 40, 50 | Structural and automotive |
| M10 | 1.5 | 17 | 20, 25, 30, 40, 50, 60 | Medium-to-high strength applications |
| M12 | 1.75 | 19 | 25, 30, 40, 50, 60, 80 | Automotive and machinery |
| M14 | 2.0 | 22 | 30, 40, 50, 60, 80, 100 | High-strength fasteners |
| M16 | 2.0 | 24 | 40, 50, 60, 80, 100, 120 | Structural and heavy-duty |
| M18 | 2.5 | 27 | 50, 60, 80, 100, 120, 150 | Heavy machinery and automotive |
| M20 | 2.5 | 30 | 60, 80, 100, 120, 150, 200 | High-load applications |
| Nominal Bolt Size | Thread Series | TPI | Major Ø (in) | Hex Head / Wrench Size* (in) | Typical Notes |
|---|---|---|---|---|---|
| 1/4″ | UNC | 20 | 0.250 | 7/16″ | General-purpose coarse thread |
| 1/4″ | UNF | 28 | 0.250 | 7/16″ | Finer pitch for better clamp control |
| 5/16″ | UNC | 18 | 0.3125 | 1/2″ | Common in machinery/fixtures |
| 5/16″ | UNF | 24 | 0.3125 | 1/2″ | Improved vibration resistance (with proper locking) |
| 3/8″ | UNC | 16 | 0.375 | 9/16″ | Structural/auto uses |
| 3/8″ | UNF | 24 | 0.375 | 9/16″ | Higher tensile area engagement |
| 7/16″ | UNC | 14 | 0.4375 | 5/8″ | Medium–heavy duty |
| 7/16″ | UNF | 20 | 0.4375 | 5/8″ | Tighter adjustment range |
| 1/2″ | UNC | 13 | 0.500 | 3/4″ | Very common structural size |
| 1/2″ | UNF | 20 | 0.500 | 3/4″ | Preferred where thread shear is critical |
| 9/16″ | UNC | 12 | 0.5625 | 13/16″ | Heavy-duty joints |
| 9/16″ | UNF | 18 | 0.5625 | 13/16″ | Finer pitch for higher preload control |
| 5/8″ | UNC | 11 | 0.625 | 15/16″ | High-load connections |
| 5/8″ | UNF | 18 | 0.625 | 15/16″ | Frequently used in automotive suspensions |
| 3/4″ | UNC | 10 | 0.750 | 1-1/8″ | Very high clamp force |
| 3/4″ | UNF | 16 | 0.750 | 1-1/8″ | Finer pitch for precision preload |
Imperial Bolt Size Chart
Hex Head / Wrench Size equals the standard across-flats (AF) dimension for ANSI/ASME hex-head bolts; socket size is the same as the wrench size.
Notes:
UNC = Unified Coarse; UNF = Unified Fine. Heavy-hex heads use larger AF than listed above. Always verify grade, lubrication, and plating before applying torque.
Speak with a CNRL engineer to find the right solution for your needs.
Bolt Installation & Torque Reference
Applying the correct torque is critical to prevent joint failure and material damage.
| Bolt Grade | Tensile Strength (MPa) | Yield Strength (MPa) | Recommended Torque Range (Nm) |
|---|---|---|---|
| 4.8 | 400 | 320 | 11.8 – 57.3 |
| 5.6 | 500 | 300 | 13.3 – 64.1 |
| 8.8 | 800 | 640 | 32.3 – 143 |
| 10.9 | 1040 | 940 | 59 – 167 |
| 12.9 | 1220 | 1100 | 95.7 – 277 |
Note:
Standard Torque Chart — M10 & M12 (values in Nm)
Get tailored fastening solutions—reach out to CNRL experts now.
Notes:
Choosing the right tools is essential for proper bolt installation. Each bolt size corresponds to a specific spanner or socket—for example, M10 bolts typically require a 17 mm wrench, while M12 bolts use 19 mm. Our reference chart makes it easy to match bolt diameters with the correct tools, reducing installation errors and preventing head damage.
We also provide drill bit and tap size guidelines to ensure accurate hole preparation and clean threads. By offering complete compatibility information, you can help customers work more efficiently and have long-term cooperation.
Partner with CNRL for trusted fastening solutions—contact us today.
Download CNRL's Product Catalog & Technical Sheets
Get instant access to our free PDF guides, including comprehensive bolt grade and size charts, along with specifications for our full range of fasteners.
Bolt Application Guide
Automotive Engine Assemblies
Use Grade 10.9 or 12.9 (metric) / SAE Grade 8 (imperial) for high strength and load-bearing reliability.
Heavy Machinery & Equipment
- Apply Grade 12.9 (metric) or SAE Grade 8 for vibration and shock resistance.
Railway & Aerospace
Require titanium bolts or lightweight high-strength alloys to balance strength and weight.
Oil & Gas / Marine Industry
Opt for A4 stainless steel or duplex steel bolts for extreme corrosion resistance.
Why Choose CNRL?
We understand that a successful project depends on more than just a product; it requires a reliable supply chain. When you partner with us, you gain access to our core manufacturing advantages:
Factory-Direct Pricing
As a factory-direct manufacturer , we eliminate middlemen, offering you a competitive price advantage on every order.
Customization Expertise
With in-house CNC machining capabilities, we can produce custom bolts to your exact specifications, including unique sizes, materials, and head types.
Reliable Supply
Our modern production linesand efficient logistics ensure on-time delivery. We manage orders with a minimum quantity of 50,000 units, guaranteeing a steady supply of high-quality fasteners for your large-scale projects.
Certified Quality
Our fasteners are produced under strict quality control and certified to international standards such as ISO, IATF, and CE, guaranteeing consistent performance and compliance for your regulated applications.
Our Partnership
1. How does CNRL ensure the quality of its high-strength bolts?
We maintain strict quality control throughout our manufacturing process, from raw material inspection to final tensile strength testing. All products are tested to meet international standards, including ISO, to guarantee performance and reliability.
2. Do you offer custom bolt sizes or materials?
Yes, we are a factory-direct OEM supplier with in-house CNC machining capabilities. We can produce custom bolts in specific sizes, materials, or finishes to meet the unique requirements of your projects.
3. Which markets does CNRL primarily export to?
Our main export markets include North America (USA), Asia (Japan), Eastern Europe (Russia), Western Europe (Italy, Germany), Australia, and South America (Brazil, Mexico). We have extensive experience serving international distributors and wholesalers.
