High-Strength Bolts vs. Ordinary Bolts: A Simple Comparison
Not all bolts are the same. High-strength bolts and ordinary bolts look similar in appearance but differ greatly in material, mechanical properties and application scenarios, so they must never be mixed up in construction. Here's what you need to know about their distinctions and proper usage rules.
What Are High-Strength Bolts?
High-strength bolts are made of high-strength steel and are tightened to a high preload (tension). They are used in critical applications like:
• Bridges
• Steel rails
• High-voltage equipment
• Pressure vessels (to ensure sealing)
These bolts tend to fail by brittle fracture, not stretching.
What Are Ordinary Bolts?
Ordinary bolts are made of regular carbon steel, without heat treatment. They are used for lighter, less critical connections. Common grades: 4.4, 4.8, 5.6, 8.8.
4 Main Differences
1. Material
High-strength: High-strength steel (45# steel, 40 boron, 20 manganese) – heat treated.
Ordinary: Carbon structural steel – no heat treatment.
2. Strength Grade
High-strength: 8.8s or 10.9s (10.9 is most common).
Ordinary: 4.4, 4.8, 5.6, 8.8.
3. How They Work (Most Important)
Ordinary bolt: Relies on shear strength of the bolt and bearing of the hole wall. The bolt fits loosely.
High-strength bolt: Uses high preload to clamp parts together, creating friction that resists movement. No slipping.
4. Reusability
High-strength bolts: Not reusable – once tightened, they cannot be reused reliably.
Ordinary bolts: Reusable – can be removed and reinstalled.
Quick Comparison Table
| Feature | High-Strength Bolt | Ordinary Bolt |
| Material | High-strength steel | Carbon steel |
| Heat treatment | Yes | No |
| Strength grade | 8.8s, 10.9s | 4.4 ~ 8.8 |
| Preload | High | Low or none |
| Force transfer | Friction (clamping) | Shear + bearing |
| Reusable? | No | Yes |
| Best for | Permanent, heavy-duty structures | Temporary or light-duty |
When to Use Which?
✅ Use High-Strength Bolts for:
• Bridges, buildings, cranes
• Vibration or earthquake zones
• Permanent connections (never disassemble)
✅ Use Ordinary Bolts for:
• Light frames, furniture, temporary fixtures
• Connections that need frequent disassembly
• Low-cost, low-stress applications
Final Takeaway
High-strength bolts = high preload, friction grip, permanent, not reusable.
Ordinary bolts = shear/bearing grip, reusable, cheaper, for lighter loads.
Never substitute ordinary bolts for high-strength bolts in critical structures. Never reuse a high-strength bolt.