Torque Wrench Calibration Guide for Thai Automotive and Industrial Factories

Why Torque Wrenches Must Be Calibrated Every 6 Months

Correct torque tightening is the difference between a safe vehicle and a dangerous one. Over-torqued bolts can strip or crack. Under-torqued bolts loosen in service. Both scenarios risk expensive product recalls. IATF 16949 Clause 7.1.5.1 requires every torque wrench used in production to have a current calibration certificate.

Types of Torque Tools

• Click-type Torque Wrench — Most common; releases with a click at the set torque value
• Beam-type — Direct reading scale; calibrated against reference torque transducer
• Digital Torque Wrench — Electronic display; calibrate both mechanical and electronic sections
• Pneumatic/Electric Power Tools — Calibrated with a dynamic torque analyzer
• Torque Screwdriver — Low-range for electronics assembly

Calibration Procedure per ISO 6789

ISO 6789-2 (Click-type)

1. Set to 20%, 60%, and 100% of nominal torque
2. Apply until the click; record the actual torque — repeat 5 times per point
3. Calculate mean; compare to setting value
4. Acceptance criterion: ±4% of nominal (or per manufacturer specification)

Recommended Calibration Frequency

Scenario	Interval
General production torque wrench	Every 6 months
After drop or impact	Immediately before returning to service
Safety-critical applications (wheels, engine)	Every 3 months or more frequently

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