Finding the right bolt size doesn't have to be complicated. Whether you're working with metric or standard (SAE) fasteners, having a reliable bolt size chart makes all the difference. This guide provides easy-to-read bolt size charts, conversions, and practical tips to help you choose the correct fastener for any application.
Why Bolt Size Matters
Using the wrong bolt size can lead to weak connections, stripped threads, structural failure, and wasted time and materials. Choosing the correct size ensures a secure fit and long-lasting performance in your projects.
Standard (SAE) Bolt Size Chart
The following chart covers the most common SAE bolt sizes used in industrial and general applications:
| Diameter (Inch) | Threads Per Inch (Coarse) | Threads Per Inch (Fine) |
|---|---|---|
| 1/4" | 20 | 28 |
| 5/16" | 18 | 24 |
| 3/8" | 16 | 24 |
| 7/16" | 14 | 20 |
| 1/2" | 13 | 20 |
| 5/8" | 11 | 18 |
| 3/4" | 10 | 16 |
Metric Bolt Size Chart
Metric bolts follow a standardized system based on millimeter measurements. Here are the most commonly stocked metric sizes:
| Diameter (mm) | Thread Pitch (mm) |
|---|---|
| M6 | 1.0 |
| M8 | 1.25 |
| M10 | 1.5 |
| M12 | 1.75 |
| M16 | 2.0 |
| M20 | 2.5 |
SAE to Metric Conversion Reference
When working across different measurement systems, use this conversion chart to find approximate equivalents:
| SAE (Inch) | Metric (Approx.) |
|---|---|
| 1/4" | M6 |
| 5/16" | M8 |
| 3/8" | M10 |
| 1/2" | M12 |
| 5/8" | M16 |
| 3/4" | M20 |
Important: These are close equivalents, but not always exact substitutes. Always verify compatibility for critical applications.
How to Read Bolt Specifications
Bolt sizes follow a standard notation that tells you everything you need to know:
SAE Example: 1/4"-20 x 2"
Metric Example: M8-1.25 x 50mm
Breaking this down: the first number is diameter, the second is thread pitch (measured in threads per inch for SAE or millimeters for metric), and the final measurement is length. Understanding this format makes selecting the correct bolt straightforward.
Selecting the Right Bolt for Your Application
Several factors influence which bolt size you need. Consider the material thickness you're fastening, the load requirements of your application, whether you need coarse or fine threads, and the environment where the bolt will be used. When in doubt, verify your measurements against a size chart or consult with a fastener specialist.
Common Sizing Mistakes to Avoid
Don't mix metric and SAE bolts in the same assembly, assume similar sizes are interchangeable, overlook thread pitch differences, or choose the wrong bolt length. These mistakes can compromise structural integrity and lead to costly rework.
Finding the Right Fastener
With a clear understanding of bolt sizing, you can quickly locate the right fastener for your project. Browse by diameter, length, thread type, and material to find exactly what you need for any application.
Keep this guide handy for quick reference whenever you're selecting fasteners. Having accurate sizing information on hand ensures secure connections and reliable performance every time.
