What is a Torque Wrench?

2025-09-08

Definition

A torque wrench is a precision tool used to accurately apply or measure torque on fasteners, such as bolts and nuts. It ensures threaded connections achieve the correct preload, preventing mechanical failures caused by over-tightening or under-tightening. Torque wrenches are essential in automotive repair, aerospace, energy, and industrial manufacturing.

Working Principle

A torque wrench measures torque through its built-in mechanism and provides visual, auditory, or tactile feedback when the applied torque reaches the preset value. Its core principles are:

  1. Utilizing the linear relationship between elastic deformation (spring or torsion bar) and applied torque.
  2. Measuring deformation or torque directly through mechanical or electronic means.
  3. Triggering a release mechanism or displaying readings when the preset value is reached.

Types of Torque Wrenches

  1. By Measurement Principle

    • Mechanical Torque Wrenches
      • Spring-loaded (most common)
      • Deflecting beam type
      • Dial indicator type
    • Electronic Torque Wrenches
      • Digital display type
      • With data logging function
      • Programmable smart type

  2. By Trigger Mechanism

    • Click-Type
      • Produces an audible "click" and handle movement when reaching the set value.
      • Most common type for industrial use
    • Beam-Type
      • Directly reads torque via a pointer and scale
      • Simple structure, requires no calibration
    • Digital-Type
      • LCD or LED display showing real-time torque
      • Allows multiple unit settings and alarms
    • Slip-Type
      • Internal mechanism slips when the set torque is reached

  3. By Direction of Use

    • One-Directional Torque Wrench - measures clockwise only.
    • Bi-Directional Torque Wrench - measures both clockwise and counterclockwise.

  4. By Accuracy Class

    • Industrial grade –±4%.
    • Precision grade –±2 ~ 3%.
    • Laboratory grade –±1%.

Applications

  • Automotive repair (tires, engines, and critical components)
  • Aerospace (aircraft structural assembly)
  • Industrial manufacturing (machine and equipment assembly)
  • Construction engineering (steel structure connections)
  • Bicycle/motorcycle maintenance

Usage Precautions

  1. Adjust the scale to the minimum value after each use
  2. Do not use as a conventional wrench
  3. Regular check its function (typically every 5,000 cycles or annually)
  4. Keep clean and avoid drops or impacts
  5. Store in a dedicated case after use

Key Purchasing Considerations

  • Select an appropriate range based on common torque requirements (recommended use within 20%-80% of capacity)
  • Consider accuracy requirements and budget
  • Pay attention to drive size (common sizes: 1/4", 3/8", 1/2", 3/4", 1")
  • Special requirements (e.g., explosion-proof, waterproof)

Conclusion

Proper use of torque wrenches significantly improves mechanical assembly quality and extends equipment lifespan, making them indispensable precision tools in modern industry.

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