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ASME B107.29-2005 — Electronic Tester, Hand Torque Tools
🔬 ASME B107.29-2005 is the American National Standard for electronic torque testers used to check manually operated hand-held torque wrenches and screwdrivers, replacing ASME B107.29M-1998. These testers act as the “reference standard” in the torque metrology chain: they electronically measure the torque output of a torque wrench or screwdriver and compare it with the set value, determining whether the tool under test meets its accuracy requirement. They are used in manufacturers’ final inspection, metrology laboratories’ periodic calibration, and corporate torque tool management. The principal change in this edition is the addition of type designators for different accuracy ratings; it was approved as an American National Standard on March 16, 2005.
💡 B107.28 (electronic torque instruments) and B107.29 (electronic testers) have a “tool vs. tool that verifies the tool” relationship: the former is used in production fastening, the latter verifies the accuracy of the former — together they close the torque quality control loop.
1. Scope and Accuracy Classification 📌
This Standard provides performance and safety requirements for electronic torque testers used for checking manually operated hand-held torque wrenches and screwdrivers. Testers are classified by drive type and accuracy class:
- Type I — Torque tester with torque-generating unit:
- Class 1: Precision accuracy ±0.25% of indicated value
- Class 2: Moderate accuracy ±0.50% of indicated value
- Class 3: Standard accuracy ±1% of indicated value
- Type II — Torque tester with hand actuation:
- Class 1: Precision accuracy ±0.25% of indicated value
- Class 2: Moderate accuracy ±0.50% of indicated value
- Class 3: Standard accuracy ±1% of indicated value
Accuracy is defined as the difference between a known applied torque and the torque displayed on the electronic indicator, measured in percentage of the known applied torque. Type I testers incorporate a torque-generating unit that applies standard torque automatically or semi-automatically; Type II testers are loaded by hand, with the operator driving the tool under test directly.
⚠️ The tester’s accuracy class must exceed the resolution needed to check the tool under test: a ±1% (Class 3) tester may suffice to check a ±2% wrench, but is clearly insufficient for a ±1% wrench. The metrological rule of thumb: the reference should be 1/3 to 1/10 of the tolerance of the unit under test.
2. Key Definitions and Measurement Concepts 📊
| Term | Definition/Note |
|---|---|
| accuracy | the difference between a known applied torque and the displayed torque, as a percentage of the known applied torque |
| peak | the maximum torque value reached during application of the load |
| first peak | the maximum torque just prior to the torque drop-off, which on Type II torque wrenches occurs as the wrench begins its momentary reduction in torque |
| rated capacity | the maximum intended torque the user shall measure or apply |
| resolution | the precision of a torque reading |
| track | continuous readout of torque applied at any moment |
| usable range of the transducer | the range to which the accuracy requirements are applied |
The “first peak” concept is critical in wrench verification: a real torque wrench (especially ratchet or overrun types) exhibits a momentary torque drop after reaching its set value. The tester must capture this “first peak” rather than the residual value after the drop, or it will underestimate the wrench’s actual output.
3. Performance Requirements and Tests 🔧
Section 5 specifies tester performance requirements and Section 6 the test procedures. Key requirements include measurement and display functions (peak-hold, first-peak capture, tracking, zeroing), meeting the accuracy error band of the applicable Class over the transducer’s usable range, operating-load limits within rated capacity, and finish, coating, and safety requirements. Verification is performed by mounting standard fixtures on the tester drive and applying programmed load sequences; readings must be stable and repeatable.
| Test/Check Item | Description | Acceptance Focus |
|---|---|---|
| Accuracy check | Apply known torques at multiple points over the usable range | Error within the applicable Class error band |
| Peak/first-peak capture | Simulate the wrench torque drop-off | Correct capture of maximum torque and first peak |
| Tracking display | Load continuously and observe readings | Continuous readout without jumps |
| Resolution check | Verify the smallest readout increment | Meets the stated resolution |
| Safety and appearance | Visual and operational check | No sharp edges, coating intact, safe operation |
4. Relationship with Related Standards 📚
B107.29 completes the B107 torque series: B107.14M (Hand Torque Tools) defines the product requirements for torque wrenches and screwdrivers; B107.28 (Electronic Torque Instruments) defines production electronic torque instruments; B107.29 defines the electronic testers that verify these tools and instruments. Referenced documents also include ASME B107.4 (driving and spindle ends) and the Hand Tools Institute “Guide to Hand Tools.” A typical corporate torque quality system works as follows: production uses hand torque tools or electronic torque instruments; on a schedule these are verified with a tester conforming to B107.29; and the verification records serve as the traceability evidence.
💡 When purchasing a tester, request a third-party calibration certificate and check it against the Standard: confirm the accuracy class (Class 1/2/3), usable range, and stated resolution, and that the certificate’s upstream standards trace to national or international measurement references.
5. Engineering Practice Essentials 🛠️
- 🔍 Selection: choose the tester Class and rated capacity based on the accuracy and torque range of the tools to be checked; for high-accuracy wrenches prefer Type I (with torque-generating unit) for stable, repeatable loading.
- 🔧 Use: zero the tester and check the transducer before use; mount the tool under test on the adapter drive, load at a uniform rate, and compare the peak reading against the set value.
- 📋 Maintenance: treat the tester as a precision metrology instrument — protect it from shock, humidity, and electromagnetic interference; send it for upstream calibration periodically.
- 📊 Records: keep a calibration file for every torque tool, recording check date, measured values, pass/fail results, and the person performing the check, forming a complete traceability chain.
6. Frequently Asked Questions ❓
❓ Q: How do I choose between Type I and Type II testers?
A: Type I has an integral torque-generating unit for stable, repeatable loading — suited to factory inspection and metrology laboratories. Type II is hand-driven, simpler, and convenient for on-site periodic checks in plant torque tool management.
A: Type I has an integral torque-generating unit for stable, repeatable loading — suited to factory inspection and metrology laboratories. Type II is hand-driven, simpler, and convenient for on-site periodic checks in plant torque tool management.
❓ Q: Why is “first peak” measurement important?
A: Most torque wrenches (especially ratchet types) momentarily drop in torque after reaching the set value. If the tester captures the post-drop value, it underestimates the actual output. First-peak measurement records the maximum before the drop, reflecting the wrench’s true trigger torque.
A: Most torque wrenches (especially ratchet types) momentarily drop in torque after reaching the set value. If the tester captures the post-drop value, it underestimates the actual output. First-peak measurement records the maximum before the drop, reflecting the wrench’s true trigger torque.
🔍 Q: Can a B107.29 tester verify electronic torque instruments (B107.28)?
A: Yes. Electronic torque instruments per B107.28 are production measurement tools whose accuracy must also be periodically verified; per traceability practice, the verifying tester’s accuracy class should be better than the instrument under test.
A: Yes. Electronic torque instruments per B107.28 are production measurement tools whose accuracy must also be periodically verified; per traceability practice, the verifying tester’s accuracy class should be better than the instrument under test.
❓ Q: How often should a tester be calibrated?
A: It depends on usage frequency and criticality. Generally send it for upstream calibration every 6–12 months, or follow the corporate metrology system and manufacturer’s recommendation; verify immediately after heavy use, drops, or overloads.
A: It depends on usage frequency and criticality. Generally send it for upstream calibration every 6–12 months, or follow the corporate metrology system and manufacturer’s recommendation; verify immediately after heavy use, drops, or overloads.
