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ASME B107.300-2010 — Torque Instruments
🔧 ASME B107.300-2010 is a consolidating standard of the ASME B107 family, Hand Tools and Accessories, that merges three previously separate torque standards — B107.14 (Hand Torque Tools, Mechanical), B107.28 (Electronic Torque Instruments), and B107.29 (Electronic Tester, Hand Torque Tools) — into a single American National Standard. It defines endurance, torque value range, and accuracy requirements for torque instruments, specifies test methods that evaluate both performance and safety, and indicates limitations of safe use. It is the key reference for designing, manufacturing, purchasing, and calibrating torque wrenches, torque screwdrivers, and electronic torque measuring devices.
💡 The consolidation unifies the chapter framework — definitions, references, performance requirements, tests, and safety requirements with limitations of use — so the earlier individual standards (B107.14/28/29) are now obsolete.
1. Scope and Product Categories 📌
B107.300 covers three categories of torque instruments:
- (a) Manually operated torque instruments: commonly used for mechanical measurement of torque to control the tightness of threaded fasteners — for example beam-type, dial, and preset (click) torque wrenches and torque screwdrivers.
- (b) Electronic torque testers: used to check manually operated hand-held torque wrenches and screwdrivers; they are the reference devices for periodic verification on the production floor and in the laboratory.
- (c) Manually operated electronic torque instruments: hand torque tools with integral or interchangeable heads that combine manual feel with electronic measurement and display.
The Standard may be used as a guide by state authorities or regulatory bodies in formulating laws or regulations, and is intended for voluntary use by establishments that use or manufacture the covered instruments — spanning automotive service, aircraft assembly, and production-line torque management.
| Category | Typical Products | Key Performance Parameters | Typical Applications |
|---|---|---|---|
| Mechanical hand torque tools | Beam/dial/click torque wrenches, torque screwdrivers | Range, accuracy (e.g., % of full scale), repeatability | Fastener tightening control, assembly work |
| Electronic torque testers | Bench-top / hand-held testers | Measurement accuracy, resolution, sampling | Periodic verification and calibration of torque tools |
| Electronic torque instruments | Integral/interchangeable-head sensor tools | Range, accuracy, digital display/alarm | Process torque control with data recording |
2. Performance Requirements: Accuracy, Range, and Endurance 📏
The Standard defines performance requirements for all three categories:
- Torque range: the instrument must provide effective torque measurement within its nominal range; the range and units (N·m, ft·lbf, in·lbf, etc.) must be clearly stated.
- Accuracy: under specified conditions, the deviation between the displayed reading and the applied torque must stay within the permitted tolerance; mechanical tools are typically rated as a percentage of full scale.
- Endurance: manually operated torque tools must survive a specified number of load/unload cycles without losing accuracy, mechanical integrity, or safety performance; click-type mechanisms in particular must verify repeatability of repeated tripping.
- Electronic characteristics: electronic testers and instruments must also meet the applicable electrical and interference requirements so that readings are stable and repeatable.
⚠️ Accuracy is only guaranteed within a specified band of the nominal range (typically 20%–100% of full scale). Near the lower limit or beyond range, readings can be significantly distorted — and this does not justify overloading the tool.
3. Test Methods and Performance Verification 🔬
Section 6 specifies the unified test procedures:
- Range and accuracy tests: load the tool to predetermined torque points and record readings to verify error, repeatability, and hysteresis.
- Endurance tests: apply repeated load/unload cycles to verify mechanism life and performance retention.
- Tester verification: produce known torque with a reference sensor or weight-and-lever system and compare the tool under test.
- Environmental tests: temperature and other condition tests, where declared, to confirm accuracy stability in practical use.
💡 Establish a periodic verification program: torque tools used on production lines should be checked against an electronic tester on a fixed cycle (e.g., weekly or monthly), and the records retained as quality-management evidence.
4. Safety Requirements and Limitations of Use 🛠️
- 🔍 Range matching: select a tool whose range covers the target tightening torque, with the target within the 20%–100% band; avoid overloading small tools.
- 🔧 Correct application: grip the middle of the handle, apply force perpendicular to the shaft, and never extend the lever arm with a cheater bar.
- 📊 No impact use: do not use a torque wrench as an impact or general loosening tool; do not use it to break loose rusted or over-tightened fasteners, which can damage the internal mechanism.
- 📋 Storage and reset: return preset torque to the lowest setting after use and store properly so the mechanism is not left under load; clean and lubricate periodically.
🚨 Torque tools are precision measuring instruments: any impact, drop, or overload causes permanent loss of accuracy. If readings become abnormal, stop use and send the tool for inspection immediately; never disassemble or hammer the internal mechanism, or tightening control may be lost and joints may fail.
5. Frequently Asked Questions ❓
❓ Q: How does B107.300 relate to the earlier B107.14, B107.28, and B107.29?
A: B107.300 consolidates them into one standard: B107.14 covered mechanical hand torque tools, B107.28 electronic torque instruments, and B107.29 electronic testers for checking hand torque tools. The prior individual editions are obsolete.
A: B107.300 consolidates them into one standard: B107.14 covered mechanical hand torque tools, B107.28 electronic torque instruments, and B107.29 electronic testers for checking hand torque tools. The prior individual editions are obsolete.
❓ Q: How often should a torque wrench be calibrated?
A: The Standard does not set a fixed interval; it requires a verification program based on usage frequency and criticality. Common practice: production-line tools are checked against an electronic tester weekly or monthly, laboratory reference tools are calibrated by third parties annually, and tools are rechecked after any accident or drop.
A: The Standard does not set a fixed interval; it requires a verification program based on usage frequency and criticality. Common practice: production-line tools are checked against an electronic tester weekly or monthly, laboratory reference tools are calibrated by third parties annually, and tools are rechecked after any accident or drop.
❓ Q: What is the difference between an electronic tester and an electronic torque instrument?
A: A tester (B107.29 class) is a reference device used to verify other tools; an electronic torque instrument (B107.28 class) is a working tool that measures torque electronically during actual tightening. They have different accuracy grades and roles and must not be interchanged.
A: A tester (B107.29 class) is a reference device used to verify other tools; an electronic torque instrument (B107.28 class) is a working tool that measures torque electronically during actual tightening. They have different accuracy grades and roles and must not be interchanged.
🔍 Q: Why must a torque wrench not be used for loosening?
A: The shock load at breakaway can exceed the structural design limit of the wrench and damage the ratchet, preset mechanism, or sensing elements, making subsequent tightening judgments unreliable. Use ordinary socket wrenches for loosening.
A: The shock load at breakaway can exceed the structural design limit of the wrench and damage the ratchet, preset mechanism, or sensing elements, making subsequent tightening judgments unreliable. Use ordinary socket wrenches for loosening.
