How to Use the Calculator
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Enter the bolt size (e.g., M10, 1/2") in the first input field. The bolt size can be either metric (M followed by diameter in mm) or imperial (e.g., 1/4", 5/8").
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Select the bolt material from the dropdown menu. Different materials have different nut factors affecting the torque calculation.
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If you know the preload force in kips, enter it in the preload field. This is optional but recommended for more accurate calculations.
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Click the Calculate button to compute the required torque.
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The calculator will display the nut factor used for the calculation and the calculated torque in lbf·ft.
Understanding the Formula
The calculator uses the formula:
Torque = K × D × F
Where:
- K = Nut Factor (depends on material and surface finish)
- D = Nominal Bolt Diameter (in inches)
- F = Preload Force (in kips)
Principle of Fastener Torque
Torque is a measure of rotational force applied to a fastener. Proper torque ensures that the fastener is tightened to the correct tension, which is crucial for:
- Preventing bolt failure under load
- Ensuring proper clamping force between connected parts
- Avoiding over-tightening which can damage threads or break the fastener
- Preventing under-tightening which can lead to leaks or connection failure
Important Notes
- The calculator provides an estimate based on standard formulas. For critical applications, always refer to manufacturer specifications.
- The nut factor (K) can vary based on surface finish and thread condition. The calculator uses typical values for common materials.
- For metric bolts, the calculator converts bolt size from mm to inches for consistency in the formula.
- The preload force affects the calculation. If you don't know the preload, you can leave this field blank, but the calculation will be less accurate.