Nut and Bolt Sizes – Thread Chart & Dimensional Guide
Nut and Bolt Sizes – Thread Chart & Dimensional Guide
Understanding nut and bolt sizes is critical in mechanical design, fastener selection, and procurement. Whether you're fabricating steel structures, assembling machines, or preparing a bill of materials, having accurate bolt dimensions ensures compatibility and safety.
This guide includes a detailed metric thread chart (M6 to M36), showing bolt diameters, thread pitch, across flat (A/F) dimensions, and standard lengths used in industrial and structural applications.
Bolt Thread Size Chart (Metric – M Series)
| Thread Size (M) | Thread Pitch (mm) | Outer Diameter (mm) | Across Flats (Hex Bolt Head) | Common Length Range (mm) |
|---|---|---|---|---|
| M6 | 1.0 | 6.0 | 10 mm | 10–60 |
| M8 | 1.25 | 8.0 | 13 mm | 16–100 |
| M10 | 1.5 | 10.0 | 17 mm | 20–120 |
| M12 | 1.75 | 12.0 | 19 mm | 30–150 |
| M16 | 2.0 | 16.0 | 24 mm | 40–200 |
| M20 | 2.5 | 20.0 | 30 mm | 50–250 |
| M24 | 3.0 | 24.0 | 36 mm | 60–300 |
| M30 | 3.5 | 30.0 | 46 mm | 80–350 |
| M36 | 4.0 | 36.0 | 55 mm | 100–400 |
Note: Pitch values shown are coarse threads as per ISO Metric standards this is only for reference . Fine threads also exist (e.g., M10 × 1.25).
Nut Sizes – Across Flats & Thickness
Matching nuts are chosen based on the bolt size. Here's a standard size chart:
| Nut Size (M) | Across Flats (mm) | Thickness (mm) |
|---|---|---|
| M6 | 10 | 5.0 |
| M8 | 13 | 6.5 |
| M10 | 17 | 8.0 |
| M12 | 19 | 10.0 |
| M16 | 24 | 13.0 |
| M20 | 30 | 16.0 |
| M24 | 36 | 19.0 |
Tip: Always ensure nut A/F matches your spanner/wrench for easy torque application.
Understanding Bolt Lengths
Bolt lengths are measured differently based on the head type:
- Hex Bolt: Length from under the head to the thread end
- Socket Head: Full length including head
- Dome/Cap Bolt: Excludes the dome for effective length
Choose bolt length based on thickness of components + washer + nut height.
Use of Standard Nut Bolt Size Charts
- Fastener selection in mechanical design
- Procurement specifications in BOQ
- Assembly drawings in manufacturing
- Maintenance and repair documentation
Frequently Asked Questions
What is the most common bolt size used in construction?M12 to M20 hex bolts are widely used in steel structures, frames, and machinery assemblies.
What size spanner fits an M16 bolt?An M16 hex bolt has a head across flats (A/F) of 24 mm, so a 24 mm spanner fits.
Are imperial and metric sizes interchangeable?No. They use different threads and head sizes. Mixing them can cause joint failure.
What is the tolerance in bolt thread sizes?Metric bolts follow ISO 965 tolerance standards. Always match with standard nuts.
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- Types of Nut and Bolt – Head & Thread Guide
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- Industrial Nuts and Bolts – Full Guide
Contact Udhhyog – Industrial Fastener Supplier in India
Need industrial-grade nuts and bolts? Udhhyog supplies a wide range of fasteners including hex bolts, structural bolts, washers, and high-tensile nuts from M6 to M36 and beyond.
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