When working on construction, machinery, or automotive projects, bolts are one of the most essential fasteners you’ll use. They come in a wide range of types and sizes, each designed to handle specific loads, threads, and materials. For many professionals, the M bolt size chart is the go-to reference.
The “M” in M bolt refers to metric measurement. Unlike bolts measured in inches, metric bolts are labeled with the letter M followed by a number that represents the bolt’s nominal diameter in millimeters. For example, an M8 bolt has an 8 mm diameter.
This guide will break down the details of the M bolt size chart, explain how to read it, and help you choose the right bolt size for your project.
What Are Metric Bolts?
Metric bolts are standardized fasteners that follow the International System of Units (SI). They are widely used across Europe, Asia, and globally in industries like construction, automotive, aerospace, and mechanical engineering.
A typical metric bolt size includes:
Nominal Diameter (M) → The diameter of the bolt shaft in millimeters.
Pitch (P) → The distance between threads, also in millimeters.
Length (L) → The measurement from the bolt head to the end of the shaft.
For example: M10 × 1.5 × 40 means a bolt with a 10 mm diameter, 1.5 mm thread pitch, and 40 mm length.
Why Use an M Bolt Size Chart?
An M bolt size chart is essential because it helps you:
Quickly identify the right bolt size for your application.
Avoid mismatched nuts and bolts.
Ensure proper load-bearing capacity.
Prevent thread damage and fitting issues.
Save time and reduce material waste in projects.
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M Bolt Size Chart (Common Sizes)
Here is a handy metric bolt size chart showing common diameters, thread pitches, and wrench sizes:
| Bolt Size | Thread Pitch (mm) | Head/Wrench Size (mm) | Typical Length Range (mm) |
|---|---|---|---|
| M3 | 0.5 | 5.5 | 6 – 50 |
| M4 | 0.7 | 7 | 8 – 60 |
| M5 | 0.8 | 8 | 10 – 70 |
| M6 | 1.0 | 10 | 12 – 120 |
| M8 | 1.25 | 13 | 16 – 150 |
| M10 | 1.5 | 16 | 20 – 200 |
| M12 | 1.75 | 18 | 25 – 250 |
| M14 | 2.0 | 21 | 30 – 300 |
| M16 | 2.0 | 24 | 35 – 320 |
| M20 | 2.5 | 30 | 40 – 400 |
| M24 | 3.0 | 36 | 50 – 500 |
| M30 | 3.5 | 46 | 60 – 600 |
| M36 | 4.0 | 55 | 70 – 600+ |
M Bolt Size Chart PDF
The M Bolt Size Chart PDF offers a detailed reference for metric bolt dimensions, including diameter, thread pitch, wrench size, and length range. Perfect for engineers, builders, and DIY enthusiasts, this chart ensures accuracy in selecting the right fasteners. It saves time, prevents mismatched bolts, and provides an easy-to-use guide for construction and mechanical applications.
How to Read the Chart
Let’s take an M10 bolt as an example:
M10 → The bolt’s nominal diameter is 10 mm.
Thread Pitch 1.5 mm → Each thread is 1.5 mm apart.
Wrench Size 16 mm → You’ll need a 16 mm spanner or socket to tighten it.
Length Range → M10 bolts are commonly available in 20 mm up to 200 mm length.
This ensures you choose the right bolt and matching nut for your project.
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Types of Metric Threads
Metric bolts can have different thread types. The most common are:
Coarse Threads (standard) – Most widely used, strong, and quick to assemble.
Fine Threads – Provide greater strength in tension and resistance to loosening.
Extra Fine Threads – Used in applications requiring very high precision, such as aerospace.
For example:
M10 × 1.5 → Coarse thread
M10 × 1.25 → Fine thread
M10 × 1.0 → Extra fine thread
Applications of Metric Bolts
Metric bolts are used in countless industries:
Construction → Fastening beams, columns, and heavy structures.
Automotive → Engine assembly, wheels, chassis, and suspension parts.
Mechanical Engineering → Machine design, tools, and industrial equipment.
Electronics → Securing small devices, panels, and housings.
Aerospace & Marine → Specialized metric bolts are used for high-stress environments.
Selecting the Right M Bolt Size
When selecting the correct bolt size, consider:
Load Requirements – Larger diameters handle higher loads.
Material – Stainless steel, carbon steel, and alloy steel offer different strengths.
Thread Pitch – Coarse threads are standard; fine threads for precision.
Environmental Conditions – Use galvanized or stainless bolts in corrosive environments.
Fit with Nut/Washer – Ensure compatibility with matching metric nuts and washers.
Advantages of Metric Bolts
Globally standardized (ISO, DIN, JIS).
Easy to measure and identify.
Wide availability in hardware stores worldwide.
Suitable for precision engineering.
Less risk of mismatched fasteners compared to inch-based bolts.
Common Mistakes to Avoid
Mixing metric and imperial bolts – They may look similar but are not compatible.
Ignoring thread pitch – Even the correct diameter won’t fit if the pitch is wrong.
Using wrong wrench size – This can damage bolt heads and reduce efficiency.
Over-tightening – May strip threads or weaken the fastener.
Conclusion
The M Bolt Size Chart is an indispensable tool for anyone working with fasteners. From small electronics to large construction projects, bolts hold the world together. Understanding bolt sizes, thread pitches, and proper applications ensures safety, durability, and efficiency in every project.
Whenever you’re unsure about which bolt to use, refer back to the M bolt size chart—it will save you time and prevent costly mistakes.
🌟 Strengthen your knowledge by visiting 👉 Bolt Size Chart: A Complete Guide
🔹 FAQs Related To M Bolt Size:
What does the ‘M’ in M bolts mean?
The ‘M’ in M bolts stands for metric, which refers to the bolt’s diameter measured in millimeters. For example, an M8 bolt has a nominal diameter of 8 mm. This metric system is globally standardized, making it easier for engineers, builders, and DIY enthusiasts to identify and use bolts accurately without confusion between different measurement systems such as inches or fractions.
How do you read M bolt sizes?
Reading M bolt sizes is simple once you know the system. For example, M10 × 1.5 × 40 means the bolt has a 10 mm diameter, a 1.5 mm thread pitch, and a 40 mm length. The first number is always the diameter, the second is the distance between threads, and the third is the bolt’s length from head to tip.
What is thread pitch in M bolts?
Thread pitch in M bolts refers to the distance between one thread and the next, measured in millimeters. For instance, a pitch of 1.5 means each thread is spaced 1.5 mm apart. Coarse pitches are standard, while fine and extra-fine pitches are used in applications requiring greater strength or precision. Correct pitch ensures proper engagement with matching nuts.
What materials are M bolts made from?
M bolts are manufactured from various materials to suit different applications. Common materials include stainless steel, galvanized steel, carbon steel, and alloy steel. Stainless steel offers corrosion resistance for outdoor or marine use, galvanized steel is durable against rust, and carbon steel is ideal for indoor applications. The material choice depends on strength, load-bearing requirements, and environmental exposure.
Where are M bolts commonly used?
M bolts are widely used in construction, automotive, mechanical, and industrial projects. In construction, they secure beams and heavy structures. In automotive applications, they hold engine parts, wheels, and suspension components. In mechanical engineering, they are essential for assembling machinery. They are also used in electronics, aerospace, and marine industries, making them versatile fasteners across multiple sectors.
How do I choose the right size M bolt?
To choose the correct M bolt size, measure the diameter of the hole or material thickness. Match it with the bolt’s nominal diameter and length. Also, check the thread pitch for compatibility with nuts. Consider the load requirements, material strength, and environmental factors like corrosion. Using an M bolt size chart simplifies the selection process and ensures accurate fitting.
Can M bolts be customized?
Yes, M bolts can be customized based on project needs. Manufacturers often provide custom options for diameter, thread pitch, and length. Special coatings such as zinc plating, galvanizing, or black oxide can also be applied for added corrosion resistance. Customized M bolts are common in specialized construction, automotive, or industrial projects where standard sizes do not meet requirements.