A shear bolt (Dutch: breekbout) is a specially engineered bolt designed to fracture at a predetermined load, acting as a mechanical safety device that protects equipment or structures from overload damage. When the applied force exceeds the bolt’s rated shear strength, the bolt breaks cleanly, disconnecting the components and preventing damage to more expensive parts.
How a shear bolt works
A shear bolt has a reduced cross-section or a machined groove at a specific point along its shank. This intentional weak point ensures the bolt fails in a controlled and predictable manner. Key characteristics include:
- Calibrated break point — the bolt is manufactured to shear at a specific torque or force value
- Clean fracture — the reduced section ensures a neat break for easy removal and replacement
- Single-use design — once broken, the bolt must be replaced with a new one of the same specification
Common types
| Type | Description |
|---|---|
| **Necked shear bolt** | Has a turned-down section on the shank that defines the break point |
| **Shear-head bolt** | The hexagonal head snaps off at a set torque, leaving a smooth tamper-resistant surface |
| **Shear pin** | A simpler cylindrical pin version used in rotating machinery |
Application
Shear bolts are used in a wide range of industries:
- Agricultural machinery — protect gearboxes and drive shafts from blockages in mowers and harvesters
- Construction equipment — safeguard hydraulic systems and mechanical linkages
- Security fixings — the bolt head shears off during installation, leaving a smooth dome that cannot be removed with standard tools
- Wind turbines — protect rotor assemblies from extreme gusts
Related Terms
- Shear pin
- Torque-limiting bolt
- Safety coupling
- Bolted connection
- Mechanical fuse
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