Bolts are one of the most common fasteners in the world, used across industries ranging from construction to automotive manufacturing. Among the many types and sizes, the M6 bolt stands out as one of the most popular choices. Its balance of size, strength, and availability makes it a go-to option for countless applications.
If you have ever assembled flat-pack furniture, worked on a bicycle, repaired an engine, or built a machine, chances are you have come across an M6 bolt. But to use it correctly, you need to understand its dimensions, standards, and variations.
This complete guide will explain what “M6” means, the standard dimensions for different lengths, head sizes, and thread pitches, along with a detailed size chart. You will also learn how to measure an M6 bolt, the different materials and grades available, and the most common uses in mechanical and DIY projects.
What Does “M6” Mean in Bolts?
The designation M6 comes from the ISO metric system of screw threads, which is the global standard for bolts and fasteners.
The “M” stands for metric thread.
The number (6) refers to the nominal diameter of the bolt in millimeters.
So, an M6 bolt has an outer thread diameter of 6 mm.
Most M6 bolts have a standard thread pitch of 1.0 mm, which means the distance between one thread and the next is exactly 1 millimeter. However, some variations exist:
M6 × 1.0 mm → Standard coarse thread
M6 × 0.75 mm → Fine thread, used where higher precision or vibration resistance is required
👉 Example: An M6 × 20 bolt means:
Diameter = 6 mm
Length = 20 mm (from under the head to the tip)
Thread pitch = 1.0 mm unless otherwise specified
Standard Dimensions of M6 Bolts
M6 bolts follow international standards such as ISO 4014, ISO 4017, and DIN equivalents. Here are the most important measurements:
1. M6 Bolt Diameter
Nominal diameter: 6.0 mm
Thread pitch: 1.0 mm (standard), 0.75 mm (fine)
2. M6 Bolt Length
Available in lengths from 6 mm to 150 mm or more.
Short bolts are commonly used in electronics and light fixtures.
Longer bolts are used in engines, heavy equipment, and structural connections.
3. M6 Bolt Head Size (Hex Head)
Across Flats (AF): 10 mm
Head Height: 4 mm
This means you would typically use a 10 mm spanner or socket to tighten or loosen an M6 hex bolt.
4. Thread Length
For bolts ≤ 125 mm: thread length is usually 2/3 of the total length
For bolts > 125 mm: thread length is about 80 mm minimum
M6 Bolt Dimension Chart (Hex Bolt – ISO 4014/4017 Standard)
| Bolt Size | Thread Pitch (mm) | Thread Diameter (mm) | Across Flats (AF) | Head Height (mm) | Typical Lengths (mm) |
|---|---|---|---|---|---|
| M6 × 10 | 1.0 | 6.0 | 10 | 4.0 | 10 |
| M6 × 16 | 1.0 | 6.0 | 10 | 4.0 | 16 |
| M6 × 20 | 1.0 | 6.0 | 10 | 4.0 | 20 |
| M6 × 25 | 1.0 | 6.0 | 10 | 4.0 | 25 |
| M6 × 30 | 1.0 | 6.0 | 10 | 4.0 | 30 |
| M6 × 40 | 1.0 | 6.0 | 10 | 4.0 | 40 |
| M6 × 50 | 1.0 | 6.0 | 10 | 4.0 | 50 |
| M6 × 60 | 1.0 | 6.0 | 10 | 4.0 | 60 |
| M6 × 80 | 1.0 | 6.0 | 10 | 4.0 | 80 |
| M6 × 100 | 1.0 | 6.0 | 10 | 4.0 | 100 |
M6 Bolt Thread Pitch Chart
| Thread Type | Pitch (mm) | Application |
|---|---|---|
| Standard | 1.0 | General fastening (most common) |
| Fine | 0.75 | Precision engineering, vibration resistance, tighter fit |
M6 Bolt Size Chart PDF
The M6 Bolt Size Chart PDF gives complete details of M6 hex bolts, covering thread pitch, diameter, head height, across flats, and standard lengths (10–100 mm). This chart helps engineers, mechanics, and DIY users choose the correct bolt size for reliable fastening in automotive, construction, and industrial applications. Download the PDF for quick and accurate reference.
Common Uses of M6 Bolts
The M6 bolt is one of the most versatile fasteners. Here are some real-world examples:
Automotive Industry – Used in engines, body panels, brake systems, and under-hood components.
Construction – Ideal for furniture assembly, timber joints, and steel frame structures.
Electronics – Secures mounting brackets, enclosures, and server racks.
Mechanical Engineering – Found in industrial machines, gear assemblies, and manufacturing equipment.
DIY Projects – Popular for bicycles, home repairs, woodworking, and hobbyist creations.
Materials & Grades for M6 Bolts
The performance of an M6 bolt depends on its material and strength grade. Different environments and loads require different types:
1. Carbon Steel Bolts
Grades: 4.6, 8.8, 10.9, 12.9
Widely used in machinery and construction
Higher grades = stronger tensile strength
2. Stainless Steel Bolts
Grades: A2-70, A4-80
Excellent corrosion resistance
Common in outdoor, marine, and food processing applications
3. Brass Bolts
Decorative and electrical applications
Non-magnetic and corrosion-resistant
4. Titanium Bolts
High strength-to-weight ratio
Used in aerospace, racing, and medical equipment
How to Measure an M6 Bolt
To correctly identify or replace an M6 bolt, measure the following:
Diameter – Across the outer threads (should be ~6 mm).
Length – From under the head to the bolt tip (for hex bolts).
Thread Pitch – Distance between threads, usually 1 mm.
Head Size – Across flats, typically 10 mm for hex head.
👉 Tip: Always use a caliper or a thread gauge for accurate measurement.
Practical Tips for Using M6 Bolts
Always use the correct spanner or socket size (10 mm for hex head) to avoid stripping.
Match the bolt grade with the application load. For high-stress applications, use 8.8 or higher.
In outdoor or humid conditions, choose stainless steel to prevent rusting.
Use washers to distribute load and prevent surface damage.
Apply thread locker (e.g., Loctite) in vibrating environments to prevent loosening.
Conclusion
The M6 bolt is one of the most commonly used fasteners worldwide, thanks to its balance of strength, size, and versatility. With a 6 mm diameter, 10 mm hex head, and a wide range of lengths and thread options, it is suitable for everything from automotive engines to home furniture.
Understanding its dimensions, materials, and grades ensures you select the right bolt for your project. Whether you are a mechanic, engineer, or DIY enthusiast, knowing how to read and use an M6 bolt size chart will save time, improve safety, and guarantee a secure connection.
Next time you reach for a bolt, check the diameter, pitch, and material—because even a small fastener like the M6 plays a critical role in keeping machines, structures, and projects together.
If you want to learn more then check this this blog post:
FAQs:
What does M6 mean on a bolt?
The term M6 refers to a metric bolt with a 6 mm nominal outer thread diameter. The “M” stands for metric thread, while “6” represents its size in millimeters. Standard M6 bolts usually have a 1.0 mm thread pitch, but fine thread versions with 0.75 mm pitch exist for precise and vibration-resistant applications.
What tool size is used for an M6 bolt?
An M6 bolt typically has a hexagonal head with an across flats (AF) measurement of 10 mm and a head height of about 4 mm. This means you would normally use a 10 mm spanner or socket wrench to tighten or loosen an M6 bolt safely without stripping or damaging the head.
What lengths are M6 bolts available in?
M6 bolts come in a wide range of lengths, from as short as 6 mm up to 150 mm or more. Shorter bolts are often used in electronics, brackets, and small assemblies, while longer M6 bolts are popular in automotive engines, industrial machines, and construction projects where secure fastening of thicker materials is needed.
What are M6 bolts commonly used for?
M6 bolts are highly versatile fasteners used in many industries. They secure automotive engine parts, brake systems, and panels. In construction, they connect timber, furniture, and metal frames. Electronics use them in enclosures and server racks. DIY enthusiasts use M6 bolts for bicycles, home repairs, and woodworking, making them a universal fastener for countless projects.
What materials are M6 bolts made from?
M6 bolts are manufactured in different materials to suit specific environments. Carbon steel (grades 4.6, 8.8, 10.9, 12.9) provides high tensile strength for mechanical uses. Stainless steel (A2-70, A4-80) resists corrosion, ideal for outdoor and marine use. Brass bolts are decorative and conductive, while titanium bolts offer exceptional strength-to-weight ratio for aerospace, racing, and medical applications.