Metric & Imperial Bolt Torque Spec Chart Lookup
Interactive fastener specification tool. Look up the recommended tightening torque for standard coarse-thread bolts across various grades and classes instantly.
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Fastener Selection
How to Use the Bolt Torque Spec Lookup
- Select the fastener measurement system (Metric or Imperial).
- Select the bolt size or diameter (e.g., M8, 3/8").
- Select the bolt grade or class (e.g., Class 8.8, Grade 5).
- Read the recommended tightening torque in both Newton-Meters (Nm) and Foot-Pounds (lb-ft).
Frequently Asked Questions
What is a Class 8.8 bolt?
Class 8.8 is a common metric bolt grade. The '8' indicates a minimum tensile strength of 800 MPa, and the '.8' indicates a yield strength of 80% of the tensile strength (640 MPa). It is roughly equivalent to a US Grade 5 bolt.
What is a Grade 8 bolt?
Grade 8 is a US standard high-strength bolt, typically used in automotive suspensions and heavy machinery. It is recognizable by 6 radial lines on the bolt head and is roughly equivalent to a Metric Class 10.9 bolt.
Why do torque specs matter?
Correct torque ensures a bolt acts as a solid spring, clamping parts together without stretching the bolt past its elastic limit (which causes shearing) or leaving it too loose (which causes vibration failure).
What is the torque spec for an M8 Class 8.8 bolt?
For a standard dry (unlubricated) M8 coarse thread bolt in Class 8.8, the general recommended torque is around 24 Nm (18 lb-ft).
Do lubricated bolts need more or less torque?
Lubricated threads (e.g., with oil, anti-seize, or threadlocker) require significantly LESS torque than dry threads to achieve the same clamping force. You typically reduce dry torque specs by 15% to 25% if using a lubricant.
Can I reuse torque-to-yield (TTY) bolts?
No. Torque-to-yield bolts (often used for cylinder heads) are permanently stretched during installation and must be replaced if removed.
How tight should a 3/8 inch Grade 5 bolt be?
A standard dry 3/8 inch Grade 5 bolt typically requires around 35 lb-ft (47 Nm) of tightening torque.
What happens if I over-torque a bolt?
Over-torquing stretches the fastener beyond its elastic limit (plastic deformation). This compromises the clamp load and frequently causes the bolt to shear off completely.
Limitations
The values provided in this calculator are standard industry guidelines for coarse-threaded, zinc-plated fasteners installed completely dry. They should be used as a reference only. If a manufacturer's service manual specifies a different torque value for a specific application, ALWAYS follow the manufacturer's specification.
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This Bolt Torque Spec Lookup tool runs entirely in your web browser. No queries or engineering specifications are sent to any external servers, ensuring complete privacy.