Hand torque tools · ISO 6789 types and classes, permissible deviation, test points and certificates
A hand torque wrench applies a controlled tightening torque to a fastener, either showing the torque reached (indicating) or signalling when a preset torque is reached (setting, such as a click wrench). Ask three things first: the torque range and drive size, the ISO 6789 type and class with its permissible deviation, and the calibration certificate supplied.
Hand torque wrenches: click and other setting wrenches, preset wrenches, and dial or digital indicating wrenches. Hydraulic torque wrenches and their pumps, electric or battery torque tools, and torque wrench testers are outside this page.
CNFX editorial research · Sources checked October 19, 2026 · 4 sources
Atlas Copco's documentation for its torque test software summarises the ISO 6789-2:2017 inspection for Type I (indicating, such as peak wrenches) and Type II (setting, such as click wrenches) tools. Five readings are taken at each target torque and the maximum deviation is 4%. For Type I and for Type II classes A, D and G there are three measurement sequences, at the tool's minimum capacity, 60% of maximum and 100% of maximum; for classes B and E the single target is the maximum capacity. For classes C and F the page is not consistent: it lists them among the classes whose target is the minimum capacity, and also says the target torque field is available only for classes C and F. Confirm the test points with the calibration laboratory. [1]
Gedore's datasheet for a Type II Class A click wrench states that the standard requires ±4% and that its wrench is calibrated to ±3%, with a traceable test certificate to DIN EN ISO 6789-2:2017. [2] Ask whether a stated accuracy is the standard's limit or a tighter maker's figure, and in which tightening direction it applies.
A study by Andreas Brüge (Acta IMEKO 4(2), 2015) on click-type torque wrenches notes that ISO 6789 sets conformity limits of ±4% and ±6% on the release value, while accredited German calibration laboratories (DAkkS) list best measurement capabilities of 0.2–1% for click-wrench calibration. It examined lever length, load rise time, temperature and humidity as influences on the release torque, noting that as a mechanical mechanism a click wrench is affected by its load history, temperature and humidity; the wrenches were stored under laboratory conditions for at least one day and given preliminary series of up to 120 releases, partly to recover lubrication after long idleness. [3]
Editorial note: Brüge's conditioning steps were for transfer wrenches used to check calibration laboratories, but the same causes apply to a workshop wrench; ask the supplier at what temperature and humidity its certificate was issued, and exercise a wrench that has been idle before use. [3]
Give the supplier the torque range and units, drive size and end fittings, type (click, preset, dial, digital), class and permissible deviation, tightening direction, certificate type, quantity and any lockable setting requirement.
02
Work out the tolerance at your setting
Gedore's example Type II Class A wrench covers 750 to 2,000 N·m with a 1-inch square drive, 50 N·m graduations a pre-set value locking device against unintentional or manipulated adjustment, and right-hand tightening; its stated working length is 920 mm and net weight 11.6 kg. [2]
Editorial calculation: for this range, the ISO 6789-2 test targets would be 750 N·m, 1,200 N·m (60% of 2,000) and 2,000 N·m. [1][2] At a 1,200 N·m setting, ±4% allows 1,152 to 1,248 N·m; the maker's ±3% narrows this to 1,164 to 1,236 N·m. [2]
Choose a range so that your usual settings fall within the calibrated span, and confirm the tolerance your joint design allows before comparing wrench classes.
03
Correct the setting when the insert tool changes the length
HAZET, a German hand-tool maker, points out that insert tools of different effective lengths alter the torque that reaches the nut or bolt, and publishes the correction it uses: MDE = (l1 + l2) × MDV ÷ (l1 + lW). Here MDE is the torque to set on the wrench in N·m, MDV the prescribed torque for the joint in N·m, l1 the length from the centre of the handle to the top in mm, l2 the gauge dimension of the insert tool the wrench was calibrated with, and lW the gauge dimension of the new insert tool. Its calculator warns when the corrected setting falls outside the wrench's permissible range, and HAZET says that in critical applications the values should be checked, where applicable with a suitable torque tester. [4]
Editorial calculation with assumed dimensions l1 = 400 mm and l2 = 17.5 mm: for a 100 N·m joint with a 100 mm open-end insert (lW = 100 mm), MDE = 417.5 × 100 ÷ 500 ≈ 83.5 N·m. Leaving the wrench at 100 N·m would put about 119.8 N·m on the joint, about 20% over, which is five times the 4% ISO 6789-2 limit. [4][1]
Editorial calculation: when the new insert is shorter than the calibration insert, the correction runs the other way; with lW = 0 mm, MDE = 417.5 × 100 ÷ 400 ≈ 104.4 N·m. [4]
Editorial note: ask the supplier for l1 and the calibration insert's gauge dimension for each wrench, and whether its calibration certificate names the insert used; record the corrected setting on the work instruction, not only the joint torque.
New insert gauge length lW (assumed l1 = 400 mm, l2 = 17.5 mm, MDV = 100 N·m)
Click, dial, digital and preset hand wrenches on the listed makers' sites
Torque-Tech lists click, slipping, dial and insulated torque wrenches; SFREYA has a torque wrench range including click wrenches with window scales; Changlu lists torque wrenches within its wrench range; Shengzhou Tengda lists adjustable, digital, dial and replaceable-head torque wrenches; Newjieli lists digital torque wrenches with torque screwdrivers; TorcStark lists a preset manual torque wrench beside its hydraulic bolting tools; Hebei Yida lists a torque wrench among its steel-bar coupler installation tools. None of these pages gives an ISO 6789-2 type, class or certificate example, so ask for them with the quotation.
05
Mechanism, scale, lock and drive head of a setting wrench
Part
Role
Fix in the order
Setting or indicating mechanism
Signals the preset torque (Type II) or shows it (Type I). [1]
Range, class, drive and conditions to fix on a torque wrench order
Example values are from the Gedore 7564-01 datasheet; temperature and humidity rows point to Brüge's findings because no reviewed wrench datasheet gives operating limits.
7 companies list this product among what they make. Company figures are quoted from each
company's own website; every card states where the relationship came from.
TORQUE-TECH PRECISION CO., LTD.
Manufacturing site to be confirmed for the order
Lists click, slipping, dial and insulated torque wrenches.
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
What is the difference between Type I and Type II torque wrenches?
Under ISO 6789-2:2017, Type I tools indicate the torque (such as peak wrenches) and Type II tools are set to a torque and signal when it is reached (such as click wrenches). [1]
How accurate must a click torque wrench be?
For Type II Class A, the standard requires ±4%; some makers calibrate tighter, for example ±3%. [2][1]
At which points is a torque wrench calibrated?
For Type I and Type II classes A, D and G: minimum capacity, 60% of maximum and maximum, with five readings at each. [1]
What affects the release torque of a click wrench?
A 2015 Acta IMEKO study tested lever length, load rise time, temperature and humidity, and conditioned wrenches with up to 120 preliminary releases because load history affects the mechanism. [3]
Do I need to change the torque setting when I use a crowfoot or open-end insert?
Yes, if its effective length differs from the insert used at calibration: HAZET corrects the setting as (l1 + l2) × prescribed torque ÷ (l1 + lW); with assumed dimensions a 100 mm insert needs about 83.5 N·m set for a 100 N·m joint (Editorial calculation). [4]
Sources and what still needs a direct check
Sources checked 2026-10-19. Atlas Copco, Gedore and HAZET are tool makers; HAZET publishes the insert-length correction formula; the Atlas Copco page summarises the ISO 6789-2 test it implements, and the Gedore datasheet is used as a worked example, not a recommendation. ISO 6789 itself is a paid standard.
