Get your fastener specs correct from the beginning. Understanding bolt sizes is essential for any DIY, hobby, or small-scale machinery venture. An incorrect size may lead to stripped threads, loose assemblies, and connection failures. Selecting the right size ensures secure fastening, dependable performance, and a durable build.
This quick-reference chart includes common bolt sizes, diameters, lengths, and thread types in both imperial and metric units. Save it as a bookmark, print it, or store it on your phone—you'll refer to it whenever you need to confirm fastener specifications.
Imperial Bolt Sizes (SAE Standard)
Imperial bolts are prevalent in North American applications, spanning from woodworking and automotive to machinery and structural work. Use this guide to identify the appropriate diameter and thread count for your project:
| Bolt Diameter | Thread Count (TPI) | Common Applications |
|---|---|---|
| 1/4" | 20 | Small metal or woodwork, light assemblies |
| 5/16" | 18 | Medium-duty tasks, general repairs |
| 3/8" | 16 | All-purpose, most frequent size |
| 1/2" | 13 | Heavy-duty or mechanical uses |
| 5/8" | 11 | Structural projects, machinery, high-load fastening |
Metric Bolt Sizes (ISO Standard)
Metric bolts are standard in global manufacturing, precision engineering, and machinery applications. If your project uses metric standards, this table covers the commonly found sizes:
| Metric Size | Thread Pitch (mm) | Common Applications |
|---|---|---|
| M4 | 0.7 | Electronics, light projects, precision work |
| M6 | 1.0 | Small assemblies, DIY projects, general fastening |
| M8 | 1.25 | General-purpose, widely used across industries |
| M10 | 1.5 | Medium-duty applications, machinery |
| M12 | 1.75 | Heavy-duty fastening, structural uses |
Choosing the Correct Bolt Size
- Match the Diameter – Your bolt should fit snugly into the hole without force or gaps. If too loose, it won't secure; if too tight, you'll strip the threads.
- Check the Length – The bolt must penetrate sufficiently and provide enough threads for nut or fastener seating. Too short won’t secure; too long wastes material and may present hazards.
- Select the Right Thread Type – Coarse threads are effective for wood and fast installation. Fine threads are better for metal and precision assemblies needing vibration resistance.
- Ensure the Right Grade – Bolt grade affects strength and load-bearing. Grade 2 suits light tasks; Grade 5 for medium duty; Grade 8 fits heavy-duty and high-stress uses.
- Pick the Material – Steel provides strength and value. Stainless steel resists corrosion in wet or outdoor settings. Brass offers non-magnetic properties for specialized needs.
Utilizing This Chart in Your Work
- Refer to it when shopping for replacement bolts or planning a new project
- Match with your project plans, manufacturer specs, or engineering drawings
- Combine size choice with material and grade to meet your load and environmental demands
- Keep this guide handy—on your phone, printed in your workshop, or bookmarked for swift reference
Discover Your Fasteners at FlangeBolts.com
After determining the size and specifications you need, explore our comprehensive inventory of quality bolts organized by diameter, length, thread type, material, and grade. Whether you're executing a quick repair or designing a complex assembly, we've got the industrial-grade fasteners to ensure you get it right the first time.
Conclusion
A bolt size chart is indispensable for any builder, engineer, or DIY enthusiast. It removes guesswork, avoids expensive errors, and ensures your assemblies are secure and reliable. Always confirm size, material, and grade against your project needs. For precision fasteners backed by quality and expertise, FlangeBolts.com has you covered.
