Torque Wrench Calibration Services
What does torque wrench calibration check?
Torque wrench calibration measures how far the torque a wrench delivers, or displays, is from the value it should deliver. We load the wrench on a torque calibration system whose transducers are traceable to NIST, at three points across its range, in each direction it is used. The deviation at each point is compared with the maximum permissible deviation in ISO 6789-1 for that wrench’s type and class.
A click wrench can keep clicking cleanly while it releases several percent away from its setting. Spring fatigue, wear in the release mechanism and storage at a high setting all shift the release point, and none of them are visible from the outside. Calibration is the only way to know the wrench still tightens fasteners to the value on the drawing.
What tolerance does ISO 6789 allow?
ISO 6789-1:2017 splits hand torque tools into Type I (indicating tools that show the applied torque) and Type II (setting tools that release or click at a preset torque). Each type has classes, and each class has its own maximum permissible deviation.
| ISO 6789 type and class | Typical tool | Max deviation above 10 N·m | At or below 10 N·m |
|---|---|---|---|
| Type II, classes A, B, C | Click and preset torque wrenches | ±4% | ±6% |
| Type II, classes D, E, F, G | Setting torque screwdrivers, flexion-bar click wrenches | ±6% | ±6% |
| Type I, classes B, C, E | Dial and digital (electronic) torque wrenches and screwdrivers | ±4% | ±6% |
| Type I, classes A, D | Beam (deflecting) wrenches, dial screwdrivers | ±6% | ±6% |
For wrenches that work in both directions, the limit applies to each direction the manufacturer specifies. If you tighten left-hand threads, the counter-clockwise direction needs calibrating too, so tell us when you order.
Which torque wrenches do you calibrate?
Click-type wrenches
Adjustable and preset click wrenches, the most common tool on production lines, in maintenance shops and in aviation.
Digital torque wrenches
Electronic wrenches with a display or data output, including models with angle measurement for torque-angle procedures.
Beam and dial wrenches
Deflecting-beam and dial-indicating wrenches, often used as the reference tool in a shop or a quality lab.
Torque screwdrivers
Low-range setting and indicating screwdrivers for electronics and medical-device assembly. See our torque screwdriver calibration guide.
We calibrate by type and range rather than by brand, so wrenches from Snap-on, CDI, Norbar, Proto, Tohnichi and other makers are handled the same way. Techmaster is an independent laboratory and is not affiliated with these manufacturers. The torque analyzers and testers that verify your wrenches can go on the same order; see torque tester calibration and digital torque meter calibration.
How is a torque wrench calibrated?
- Inspection. We check the square drive, ratchet, scale, battery and release mechanism, and record anything that would affect the result.
- Exercising. Setting wrenches are cycled at full scale before measurement so the mechanism settles, as ISO 6789 requires.
- As-found test. Readings at 20%, 60% and 100% of the range, in each direction of use, on a NIST-traceable torque calibration system.
- Adjustment. If any point is outside the ISO 6789 limit and the design allows it, we adjust the wrench.
- As-left test and certificate. The wrench is measured again and you receive an ISO/IEC 17025 accredited certificate.
How often should a torque wrench be calibrated?
ISO 6789-2 suggests recalibration after about 12 months or 5,000 operations, whichever comes first, when your quality system does not set its own interval. High-use production wrenches can reach 5,000 cycles in a few months. Recalibrate early after a drop, an overload, a repair, or any use as a breaker bar. Our guide on how often to calibrate a torque wrench covers setting intervals from your as-found history.
What is on the calibration certificate?
- Wrench identification, ISO 6789 type and class, range and direction(s) tested
- As-found and as-left readings at each test point, with the deviation from the target value
- Measurement uncertainty at each point, and the decision rule behind the pass or fail statement
- The reference standards used and their traceability to NIST
- Laboratory conditions, date, technician and the ANAB accreditation mark (certificate AC-1736)
Our guide to reading an ISO 17025 calibration certificate explains each field, and accredited vs NIST-traceable calibration explains why the accreditation mark matters in an audit.
Where is torque calibration accredited?
Torque is on Techmaster’s ANAB ISO/IEC 17025 accredited scope (certificate AC-1736) at four laboratories. San Antonio holds the highest accredited torque range, up to 1,000 lbf·ft. Ranges and uncertainties for each lab are listed on our accreditation scope.
| Laboratory | Torque on accredited scope | Location page |
|---|---|---|
| Vista, CA (San Diego HQ) | Yes | Lab locations |
| Santa Clara, CA (Silicon Valley) | Yes | Santa Clara lab |
| Orlando, FL | Yes | Orlando lab |
| San Antonio, TX | Yes, up to 1,000 lbf·ft | San Antonio lab |
Ask us about pickup, drop-off, expedited turnaround and on-site torque calibration for your location.
How do you keep a torque wrench accurate between calibrations?
- Store click wrenches at the lowest setting on the scale, never at a high setting.
- Work between 20% and 100% of the range; the calibration does not cover readings below 20%.
- Never use a torque wrench to loosen seized fasteners or as a breaker bar.
- Pull on the handle grip, slowly and square to the wrench, and stop at the click.
- Send the wrench in straight away after a drop, and review work done since if the as-found result is out of tolerance.
Torque wrench calibration FAQ
How much does torque wrench calibration cost?
How often should a torque wrench be calibrated?
What tolerance does a click torque wrench have to meet?
Do you calibrate digital torque wrenches?
Which Techmaster labs are accredited for torque?
Can you adjust a torque wrench that fails calibration?
Need torque wrench calibration?
Send the make, model, range and quantity. We reply with a quote and the nearest accredited lab.
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Khanh Nguyen is the Marketing Manager at Techmaster Electronics, a B2B marketing leader covering the test, measurement, and ISO/IEC 17025 accredited calibration industry across the US and Vietnam markets.