oSIST prEN ISO 6789-2:2025

Assembly tools for screws and nuts - Hand torque tools - Part 2: Requirements for calibration and determination of measurement uncertainty (ISO/DIS 6789-2:2025)

This document specifies the method for the calibration of hand torque tools and describes the method of calculation of measurement uncertainties for the calibration.
It also specifies the minimum requirements for a certificate of calibration to this standard for hand torque tools.
The Annex C of this document specifies the minimum requirements for the calibration of the torque measurement device where the relative measurement uncertainty interval, W´md, is not already provided by a traceable calibration certificate.
This document applies to hand torque tools which are classified as indicating torque tools (Type I) and setting torque tools (Type II).
NOTE    Hand torque tools covered by this document are those identified in ISO 1703:2018 by reference numbers 7 1 00 01 0 to 7 1 00 14 0 inclusive.  Torque limiting hand torque tools do not yet have reference numbers and will not do so until the next revision of ISO 1703

Outils de manoeuvre pour vis et écrous - Outils dynamométriques à commande manuelle - Partie 2: Exigences d'étalonnage et détermination de l'incertitude de mesure (ISO/DIS 6789-2:2025)

ISO 6789-2:2017 spécifie la méthode d'étalonnage des outils dynamométriques à commande manuelle et décrit la méthode de calcul des incertitudes de mesure associées à l'étalonnage.
ISO 6789-2:2017 spécifie les exigences minimales relatives à l'étalonnage du dispositif de mesure de couple lorsque l'intervalle d'incertitude de mesure relative, W´md, n'est pas déjà fourni par un certificat d'étalonnage traçable.
L'ISO 6789 s'applique à l'étalonnage pas à pas (statique) et continu (quasi-statique) des dispositifs de mesure de couple, dont le couple est établi en mesurant la variation élastique d'un corps déformable ou une variable mesurée proportionnelle au couple.
ISO 6789-2:2017 s'applique aux outils dynamométriques à commande manuelle classés en tant qu'outils dynamométriques à lecture directe (Type I) et outils dynamométriques à déclenchement (Type II).
NOTE Les outils dynamométriques à commande manuelle couverts par le présent document sont ceux identifiés dans l'ISO 1703:2005 sous les numéros de référence 6 1 00 11 0, 6 1 00 11 1 et 6 1 00 12 0, 6 1 00 12 1 et 6 1 00 14 0, 6 1 00 15 0. L'ISO 1703 est en cours de révision. Dans la prochaine édition, les outils dynamométriques seront traités dans un article distinct, et du fait de cette modification, les numéros de référence changeront également et des numéros de référence supplémentaires seront ajoutés.

Orodja za vijake in matice - Ročna vrtilna orodja - 2. del: Zahteve za umerjanje in določanje merilne negotovosti (ISO/DIS 6789-2:2025)

General Information

• Status: Not Published
• Public Enquiry End Date: 14-Sep-2025
• ICS: 25.140.30 - Hand-operated tools
• Technical Committee: I13 - Imaginarni 13
• Current Stage: 4020 - Public enquire (PE) (Adopted Project)
• Start Date: 23-Jul-2025
• Due Date: 10-Dec-2025
• Completion Date: 15-Sep-2025
• Ref Project: prEN ISO 6789-2 - Assembly tools for screws and nuts - Hand torque tools - Part 2: Requirements for calibration and determination of measurement uncertainty (ISO/DIS 6789-2:2025)

Relations

• Revises: SIST EN ISO 6789-2:2017 - Assembly tools for screws and nuts - Hand torque tools - Part 2: Requirements for calibration and determination of measurement uncertainly (ISO 6789-2:2017)
• Effective Date: 05-Apr-2023

Overview

The oSIST prEN ISO 6789-2:2025:2025 standard, titled "Assembly Tools for Screws and Nuts - Hand Torque Tools - Part 2: Requirements for Calibration and Determination of Measurement Uncertainty", is developed by CEN to specify the calibration methods and measurement uncertainty calculations for hand torque tools. This document focuses on both indicating torque tools (Type I) and setting torque tools (Type II) used in manual assembly tasks involving screws and nuts. It provides minimum requirements for calibration certificates, ensuring that torque tools meet precision and quality standards crucial for industrial, technological, and commercial applications.

This forthcoming international standard outlines comprehensive procedures for the accurate calibration of torque tools and the reliable estimation of measurement uncertainties, reinforcing product consistency and safety in mechanical assembly processes.

Key Topics

• Calibration Methodology for Hand Torque Tools
  The standard details step-by-step calibration processes to verify the performance of hand torque tools, including orientation considerations, loading methods, and loading sequences to ensure accuracy in torque application.

• Measurement Uncertainty Determination
  Comprehensive guidance on calculating both relative standard measurement uncertainty and expanded measurement uncertainty to quantify the reliability of torque measurements during calibration.

• Certificate of Calibration Requirements
  Specifies the minimum content and format requirements for calibration certificates to promote transparency and traceability in torque tool verification.

• Torque and Angle Calibration Specifics
  Covers precise methods for calibrating not only torque values but also angle measurements, recognizing the increasing use of angle functions in advanced torque tools.

• Minimum Requirements for Calibration of Measurement Devices
  Annex C introduces requirements for the calibration of torque measurement devices when traceable uncertainty values are unavailable, ensuring robust secondary calibration capabilities.

• Types of Tools Covered
  The standard applies to torque tools identified according to ISO 1703 reference numbers 7 1 00 01 0 to 7 1 00 14 0 inclusive, excluding torque limiting hand torque tools awaiting future classification.

Practical Applications

• Manufacturers of Hand Torque Tools
  Ensure compliance with international calibration standards during production and supply calibration certificates meeting ISO 6789-2 requirements for customers.

• Calibration Laboratories
  Provide accredited calibration services adhering to the standardized calibration methodology and uncertainty calculation for hand torque tools, supporting quality assurance and regulatory compliance.

• Industrial Assembly Operations
  Utilize torque tools calibrated per ISO 6789-2 to guarantee accuracy and repeatability of torque application, which is critical in automotive, aerospace, electronics, and machinery manufacturing.

• Quality Control and Maintenance
  Facilitate routine verification and recalibration of torque tools as part of preventive maintenance regimes, ensuring ongoing tool accuracy and prolonging tool service life.

• Regulatory and Compliance Bodies
  Reference this standard for certification and assessment processes relating to torque application tools, helping enforce quality and safety standards in manufacturing environments.

Related Standards

• ISO 6789-1: Specifies design and quality control requirements for hand torque tools along with manufacturers’ declarations of conformance.
• ISO 6789-3: Defines verification and performance reporting requirements for torque tools, aimed at routine compliance checks rather than complete calibration.
• ISO 1703: Provides the classification and identification system for hand tools, referenced to specify applicable torque tool types.
• ISO/IEC Directives: Governs the editorial and procedural framework for developing ISO standards, ensuring consistency and intellectual property compliance.

By adhering to oSIST prEN ISO 6789-2:2025:2025, stakeholders in hand torque tool manufacturing and calibration can expect improved calibration accuracy, standardized measurement uncertainty evaluation, and enhanced confidence in the performance of hand torque tools critical to fastener assembly quality and safety.

Standards Content (Sample)

SLOVENSKI STANDARD
01-september-2025
Orodja za vijake in matice - Ročna vrtilna orodja - 2. del: Zahteve za umerjanje in
določanje merilne negotovosti (ISO/DIS 6789-2:2025)
Assembly tools for screws and nuts - Hand torque tools - Part 2: Requirements for
calibration and determination of measurement uncertainty (ISO/DIS 6789-2:2025)
Outils de manoeuvre pour vis et écrous - Outils dynamométriques à commande
manuelle - Partie 2: Exigences d'étalonnage et détermination de l'incertitude de mesure
(ISO/DIS 6789-2:2025)
Ta slovenski standard je istoveten z: prEN ISO 6789-2
ICS:
25.140.30 Orodja za ročno uporabo Hand-operated tools
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 6789-2
ISO/TC 29/SC 10
Assembly tools for screws and
Secretariat: DIN
nuts — Hand torque tools —
Voting begins on:
Part 2: 2025-06-23
Requirements for calibration and
Voting terminates on:
2025-09-15
determination of measurement
uncertainty
Outils de manoeuvre pour vis et écrous — Outils
dynamométriques à commande manuelle —
Partie 2: Exigences d'étalonnage et détermination de l'incertitude
de mesure
ICS: 25.140.30
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 6789-2:2025(en)
DRAFT
ISO/DIS 6789-2:2025(en)
International
Standard
ISO/DIS 6789-2
ISO/TC 29/SC 10
Assembly tools for screws and
Secretariat: DIN
nuts — Hand torque tools —
Voting begins on:
Part 2:
Requirements for calibration and
Voting terminates on:
determination of measurement
uncertainty
Outils de manoeuvre pour vis et écrous — Outils
dynamométriques à commande manuelle —
Partie 2: Exigences d'étalonnage et détermination de l'incertitude
de mesure
ICS: 25.140.30
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
CH-1214 Vernier, Geneva
NOTIFICATION OF ANY RELEVANT PATENT
Phone: [phone]
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 6789-2:2025(en)
ii
ISO/DIS 6789-2:2025(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions .2
3.2 Symbols, designations and units .3
4 General requirements for torque calibration and angle calibration . 4
4.1 Calibration by the manufacturer of the torque tool .4
4.2 Calibration during use .4
4.3 Ambient conditions.5
4.4 Calibration system .5
5 Torque calibration - specific requirements . 6
5.1 Torque measurement - application .6
5.1.1 Orientation of torque tools to be calibrated .6
5.1.2 Loading methods for torque tools to be calibrated .8
5.2 Torque measurement – loading sequence .9
5.2.1 General .9
5.2.2 Preloading sequence .9
5.2.3 Loading sequence .10
5.3 Torque measurement - error . .10
5.4 Torque measurement - sources of uncertainty .11
5.4.1 General .11
5.4.2 Evaluation of Type B uncertainties due to the torque tool .11
5.4.3 Evaluation of Type A uncertainty due to the torque tool .17
6 Torque measurement - determination of the result .18
6.1 Determination of the relative standard measurement uncertainty, w .18
6.2 Determination of the relative expanded measurement uncertainty, W .19
6.3 Determination of the relative measurement uncertainty interval, W ‘ .19
7 Angle calibration – specific requirements . 19
7.1 Angle measurement -application .19
7.2 Angle measurement - loading sequence . 20
7.2.1 General . 20
7.2.2 Loading sequence . 20
7.2.3 Ratcheting function .21
7.3 Angle measurement .21
7.3.1 Measurement error .21
7.3.2 Error due to bending of the tool . 22
7.3.3 Evaluation of Type B angle measurement uncertainties due to the torque tool . 22
7.3.4 Evaluation of Type B angle measurement uncertainties due to the torque tool . 22
8 Angle measurement - determination of the result .23
8.1 Determination of the relative standard measurement uncertainty,w . 23
8.2 Determination of the relative expanded measurement uncertainty, W .24
8.3 Determination of the relative measurement uncertainty interval, W ‘ .24
9 Calibration certificate .24
Annex A (informative) Calculation example for an indicating torque tool (Type I) .26
Annex B (informative) Calculation example for a setting torque tool (Type II) .33
Annex C (informative) Minimum requirements for the calibration of the torque measurement
device and the estimation of its measurement uncertainty .39

iii
ISO/DIS 6789-2:2025(en)
Annex D (informative) Calculation example for a torque tool with angle .40
Bibliography .46

iv
ISO/DIS 6789-2:2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the World
Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following URL:
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 29, Small tools, Subcommittee SC 10, Assembly
tools for screws and nuts, pliers and nippers.
The new edition of ISO 6789-2, together with revisions of ISO 6789-1 and the addition of ISO 6789-3, cancel
and replace ISO 6789-1:2017 and ISO6789-2:2017 which have been technically revised with changes as
follows. ISO 6789-1:2017 has been divided into two parts. The requirements for design and quality control
during manufacture as well as the manufacturer’s Declaration of Conformance are now solely aimed at
manufacturers and remain in ISO 6789-1. The minimum requirements for conformance checking of tools
during use are moved to the new ISO 6789-3.
Minimum requirements for calibration are still found in this standard ISO 6789-2
A list of all parts in the ISO 6789 series can be found on the ISO website.

v
ISO/DIS 6789-2:2025(en)
Introduction
This revision has incorporated user feedback on the following general topics.
Clarifying for users of the standard which parts they should purchase to carry out their work related to
hand torque tools. (See below)
Achieving a significant reduction in the number of uncertainty measurements required to provide a
calibration certificate
Separating the declaration of conformance issued by a manufacturer from the performance report issued
by a test house or internal quality control function.
The calibration or verification of angle measurements found in a growing number of torque tools
The addition of tools that can be either indicating or setting according to the customer need.
The three parts of ISO 6789 that result from this revision can be summarised as follows:
ISO 6789-1 continues to provide designers and manufacturers with relevant minimum requirements
for the development and documentation of hand torque tools. The manufacturer may choose the level of
documentation supplied with the tool according to the typical needs of the manufacturer’s customers.
This could be a certificate of calibration according to ISO 6789-2 or a verification report according to
ISO 6789-3
ISO 6789-2 provides manufacturers and calibration laboratories with requirements for both torque and
angle calibrations of hand torque tools together with streamlined methods for the calculation of uncer-
tainties. Additionally, minimum requirements for the calibration of torque measurement devices as an
alternative when national standards are not available, are described in ISO 6789-2, Annex C
ISO 6789-3 provides basic requirements for verifying and reporting whether the torque tool complies
with the torque performance requirements of ISO 6789-1. It has been created as a separate standard to
make it more accessible to users who are not torque tool manufacturers. The verification defined in ISO
6789-3 does not have as much detailed information, so does not provide the same degree of confidence
in the performance of the torque tool, as a calibration certificate defined in ISO 6789-2.
The following scenarios may be of help in assisting users of the ISO 6789 series to identify the appropriate
part(s) applicable to their activities:
Customer requires a torque tool with an accredited calibration certificate in order to meet legislative or
commercial requirements. Solution is to purchase a torque tool and submit it to an accredited calibration
laboratory for a Certificate of Calibration. (Note: Some torque tool manufacturers may offer such a service.)
The calibration should be according to ISO6789-2. The torque tool will be supplied with a Manufacturer’s
Declaration of Conformance that the tool complies with the design requirements of ISO 6789-1
Customer requires a calibration certificate in order to understand the technical performance of the torque
tool. Solution is to purchase a torque tool that is supplied with a Certificate of Calibration. If such a product
is not readily available, then a torque tool with a Performance Verification Report according to ISO6789-3
can be purchased and submitted to a calibration laboratory for calibration according to ISO6789-2. The
torque tool will be supplied with a manufacturer’s Declaration of Conformance that the tool complies with
the design requirements of ISO 6789-1
Customer does not have any legislative, commercial or technical constraints but would still like some
confirmation that the torque tool will perform with the level of accuracy required. Solution is to purchase
a torque tool that has a Manufacturer’s Declaration of Conformance confirming that the tool has been
designed and tested during development in accordance with ISO 6789-1 and is provided with a Performance
Verification Report that shows the accuracy level of that specific tool. The lack of the above constraints
should not deter the customer from obtaining the increased information and legal protection that comes
with a Calibration Certificate compared with a Performance Verification Report.

vi
DRAFT International Standard ISO/DIS 6789-2:2025(en)
Assembly tools for screws and nuts — Hand torque tools —
Part 2:
Requirements for calibration and determination of
measurement uncertainty
1 Scope
This document specifies the method for the calibration of hand torque tools and describes the method of
calculation of measurement uncertainties for the calibration.
It also specifies the minimum requirements for a certificate of calibration to this standard for hand torque tools.
The Annex C of this document specifies the minimum requirements for the calibration of the torque
measurement device where the relative measurement uncertainty interval, W´ , is not already provided by
md
a traceable calibration certificate.
This document applies to hand torque tools which are classified as indicating torque tools (Type I) and
setting torque tools (Type II).
NOTE Hand torque tools covered by this document are those identified in ISO 1703:2018 by reference
numbers 7 1 00 01 0 to 7 1 00 14 0 inclusive. Torque limiting hand torque tools do not yet have reference numbers and
will not do so until the next revision of ISO 1703
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
3 Terms, definitions and symbols
For the purposes of this document, the terms and definitions given in ISO 6789-1 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https:// www .electropedia .org/
— ISO Online browsing platform: available at https:// www .iso .org/ obp

ISO/DIS 6789-2:2025(en)
3.1 Terms and definitions
3.1.1
calibration
operation that, under specified conditions, in a first step, establishes a relation between the quantity values
with measurement uncertainties provided by measurement standards and corresponding indications with
associated measurement uncertainties and, in a second step, uses this information to establish a relation for
obtaining a measurement result from an indication
Note 1 to entry: A calibration may be expressed by a statement, calibration function, calibration diagram, calibration
curve, or calibration table. In some cases, it may consist of an additive or multiplicative correction of the indication
with associated measurement uncertainty.
Note 2 to entry: Calibration should not be confused with adjustment of a measuring system, often mistakenly called
“self-calibration”, nor with verification of calibration.
Note 3 to entry: Often, the first step alone in the above definition is perceived as being calibration.
[SOURCE: ISO/IEC Guide 99:2007, 2.3.9]
3.1.2
calibration system
combination of a measurement device and the loading system for application of torque or angle that acts as
the measurement standard for the hand torque tool
Note 1 to entry: A calibration system can also be used as a measurement system as defined in ISO 6789-1.
3.1.3
calibration laboratory
facility that has internal systems of quality control including controls over environment, operators and
processes and which can demonstrate traceability of the reference measurement standard to national or
international standards
3.1.4
accredited calibration laboratory
laboratory with formal recognition by an accrediting organization that the laboratory is competent to carry
out specific activities which lead to the calibration of systems in accordance with documented requirements
of the accrediting organization
3.1.5
measurement device
working measurement standard provided by an electronic torque transducer or angle encoder and display
3.1.6
measurement error
measured quantity value minus a reference quantity value
[SOURCE: ISO/IEC Guide 99:2007, 2.16, modified — Notes 1 and 2 to entry have been omitted.]
3.1.7
reference measurement standard
measurement standard designated for the calibration of other measurement standards for quantities of a
given kind in a given organization or at a given location
[SOURCE: ISO Guide 99:2007, 5.6]
3.1.8
reproducibility
condition of measurement, out of a set of conditions that includes different locations, operators, measuring
systems, and replicate measurements on the same or similar objects
[SOURCE: ISO Guide 99:2007, 2.24]

ISO/DIS 6789-2:2025(en)
3.1.9
Type A evaluation (of uncertainty)
method of evaluation of uncertainty by the statistical analysis of series of observations
Note 1 to entry: These data are taken directly from the measurements obtained during calibration of each torque tool
and cannot be prepared in advance.
[SOURCE: ISO/IEC Guide 98-3:2008, 2.3.2, modified — Note 1 to entry has been added.]
3.1.10
Type B evaluation (of uncertainty)
method of evaluation of uncertainty by means other than the statistical analysis of series of observations
[SOURCE: ISO/IEC Guide 98-3:2008, 2.3.3]
3.2 Symbols, designations and units
The designations used in this document are indicated in Table 1.
Table 1 — Symbols, designations and units
Symbol Designation Unit
a Calculated relative measurement error of the torque tool for the calibration torque %
s
a Mean value of the relative measurement error at each calibration torque %
s
b Stated measurement error of the measurement device N∙m
e
b Stated relative measurement error of the measurement device %
ep
Variation due to geometric effects of the interface between the output drive of the torque
b N∙m
int
tool and the calibration system
b Variation due to the variation of the force loading point N∙m
l
b Variation due to geometric effects of the output drive of the torque tool N∙m
od
b Variation due to the repeatability of the torque tool N∙m
re
Variation due to the reproducibility of the torque tool (Type I and Type II Classes A, D
b N∙m
rep
and G only)
Θ Indicated value of angle on torque tool °
a
Θ Indicated value of angle on reference device °
r
a Relative angle measurement error at each calibration point %
Θ
Coverage factor applied to the relative measurement uncertainty to achieve a confidence
k —
level of approximately 95 %
r Resolution of the display (Type I and Type II Classes A, D and G only) N∙m
Maximum limit value of the measurement range of the torque tool declared by the man-
T N∙m
max
ufacturer
Minimum limit value of the measurement range of the torque tool declared by the man-
T N∙m
min
ufacturer
w Relative standard measurement uncertainty of the torque tool at the calibration torque %
w Relative standard angle measurement uncertainty of the torque tool at the calibration torque
a
w Component of w due to the bending of the tool structure under torque while measuring angle
ben
Component of w due to geometric effects of the interface between the output drive of the
w %
int
torque tool and the calibration system
Component of w due to the length variation of the force loading point from the centre of
w %
l
tool rotation
w Component of w due to geometric effects of the output drive of the torque tool %
od
Relative standard measurement uncertainty due to resolution of the display of the torque
w %
r
tool (Type I and Type II Classes A, D and G only)
NOTE While N∙m is the unit commonly used, the output signal can be detected in various units, e.g. voltage.

ISO/DIS 6789-2:2025(en)
TTabablele 1 1 ((ccoonnttiinnueuedd))
Symbol Designation Unit
w Component of w due to the variation in angle measurement when rotating as slow speed %
ss
w Component of w due to the variation in stability of angle measurement when stationary %
st
w Component of w due to repeatability of the torque tool %
re
w Component of w due to angle repeatability of the torque tool %
re,a
Component of w due to reproducibility of the torque tool (Type I and Type II Classes A,
w %
rep
D and G only)
W Relative expanded measurement uncertainty of the torque tool at the calibration torque %
W′ Relative measurement angle uncertainty interval of the torque tool at the calibration torque %
Relative expanded measurement angle uncertainty of the torque tool at the calibration
Wa %
torque
W′ Relative measurement uncertainty interval of the torque tool at the calibration torque %
a
NOTE While N∙m is the unit commonly used, the output signal can be detected in various units, e.g. voltage.
Table 2 — Type, Class and Description of Hand Torque Tools
Class Type Description
I A Wrench, torsion or flexion bar
I B Wrench, rigid housing, with scale or dial or display
I C Wrench, rigid housing and electronic measurement
I D Screwdriver, with scale or dial or display
I E Screwdriver, with electronic measurement
II A Wrench, adjustable, graduated or with display;
II B Wrench, fixed adjustment
II C Wrench, adjustable, non-graduated
II D Screwdriver, adjustable, graduated or with display
II E Screwdriver, fixed adjustment
II F Screwdriver, adjustable, non-graduated
II G Wrench, flexion bar, adjustable, graduated
II H Wrench, torque limiting, adjustable, graduated
II J Wrench, torque limiting, fixed adjustment
II K Wrench, torque limiting, adjustable, non-graduated
4 General requirements for torque calibration and angle calibration
4.1 Calibration by the manufacturer of the torque tool
ISO 6789-1 allows the manufacturer to choose the format of documentation provided with a new torque
tool in addition to the Manufacturer’s Declaration of Conformance. The needs of users should be considered
in choosing to offer either a Certificate of Calibration, according to ISO 6789-2, or a Verification Report
according to ISO 6789-3. Where the torque tool also is capable of measuring angle, the angle performance
shall be included in the documentation.
If a Certificate of Calibration is chosen, the calibration may be performed as part of the production process
or in a separate calibration laboratory. The calibration shall comply with the requirements of this standard.
4.2 Calibration during use
If the user utilizes procedures for the control of test devices, torque tools shall be included in these
procedures. The interval between calibrations shall be chosen based on the factors of operation such as

ISO/DIS 6789-2:2025(en)
required maximum permissible measurement error, frequency of use, typical load during operation as well
as ambient conditions during operation and storage conditions. The interval shall be adapted according
to the procedures specified for the control of test devices and by evaluating the results gained during
successive calibrations.
If the user does not utilize a control procedure, a period of 12 months, or 5 000 cycles, whichever occurs
first, may be taken as default values for the interval between calibrations. The interval starts with the first
use of the torque tool.
Shorter interval between calibrations may be used if required by the user, their customer or by legislation.
The torque tool shall be calibrated when it has been subjected to an overload greater than 125 % of the
maximum capacity of the tool, after repair, or after any improper handling which might influence the torque
tool performance and the fulfilment of the quality conformance requirements.
4.3 Ambient conditions
The measurement procedure shall be carried out at an ambient temperature held constant to within ±1 K.
This temperature shall be between 18 °C and 28 °C at a maximum relative humidity of 90 % and shall be
documented.
Prior to measurement, the measurement device and the torque tool shall be allowed to acclimatise to the
ambient temperature and humidity.
4.4 Calibration system
The calibration system shall be chosen to be suitable for the measurement of the specified range of the
torque tool and will comply with the requirements of this clause.
Torque and angle measurement devices shall have a valid calibration certificate traceable to a national
standard or to a calibration laboratory meeting the requirements of ISO/IEC 17025. The torque calibration
shall be performed to a recognised national or regional standard for the calibration of torque measurement
devices, or, in the absence of such a standard, according to Annex C of this standard.
If the user does not utilize a control procedure, a period of 24 months shall be the maximum interval
between calibrations. The measurement device shall be re-calibrated if it was exposed to an overload
larger than 20 % of T , after a repair has been carried out or after an improper use which can influence the
E
measurement uncertainty.
At each target value of torque, the relative uncertainty interval, W ‘ , of the respective measurement
mdT
device shall not exceed 1/4 of the expected maximum relative uncertainty interval of the torque tool, W ‘ .
T
At each target value of angle, the absolute angle uncertainty interval, W ‘ , of the respective measurement
mdA
device should not exceed 1/4 of the expected maximum absolute uncertainty interval of the torque tool, W ’
A.
Note The achievable angle measurement uncertainty will depend upon the angle measurement method chosen.
See Clause 7
The uncertainty intervals of the measurement device and the torque tool shall be stated in the calibration
certificate.
ISO/DIS 6789-2:2025(en)
5 Torque calibration - specific requirements
5.1 Torque measurement - application
The torque shall be applied by means of one of the following methods.
a) The torque tool is caused to rotate about the torque measurement device axis by the following:
1. for torque wrenches, a force or two forces with equal value and opposite direction for T-handles,
applied to the handle of the tool at a constant radial distance;
2. for torque screwdrivers, a torque applied to the handle of the tool or two forces with equal value
and opposite direction for T-handles.
b) The torque measurement device rotates on its measuring axis while a reaction force is applied to the
handle of the torque tool.
5.1.1 Orientation of torque tools to be calibrated
Torque wrenches to be measured shall be positioned in one of the orientations shown in Figure 1a, 1b, 1c.
The orientation shall be documented by reference to the tool position and the measurement axis within the
Calibration Certificate.
Torque screwdrivers to be measured shall be positioned in line with the measurement axis of the torque
measurement device in either the horizontal or vertical axis shown in Figure 1d and 1e.
Figure 1a — Testing of a tool in a vertical position with horizontal measuring axis
Figure 1b — Testing of a tool in a horizontal position with vertical measuring axis

ISO/DIS 6789-2:2025(en)
Figure 1c — Testing of a tool in a horizontal position with horizontal measuring axis
Figure 1d — Testing of a torque screwdriver in a horizontal position with horizontal measuring axis

a
Torque measurement device.
b
Axis of rotation.
c
Orientation of torque tool.
Figure 1e — Testing of a torque screwdriver in a vertical position with vertical measuring axis

ISO/DIS 6789-2:2025(en)
5.1.2 Loading methods for torque tools to be calibrated
The torque tool may be loaded, or the reaction force provided, either by machine or by hand. The calculation
of the uncertainty associated with the calibration will consider the loading method.
Whilst highly skilled operators can perform reasonably consistent loading of torque tools, they are still
subject to fatigue and other distractions that are not present in machine loading. Less skilled operators will
show a higher variation in loading and observation of target values, especially for Type I torque tools.
The effect of operator variability shall be evaluated by users of this standard who wish to calibrate torque
tools by hand. Requirements are detailed in 5.4.2.9.
The connection between the loading system, whether by machine or by hand, and the torque tool, shall
permit self-alignment of the tool so that parasitic forces and moments are minimized.
For torque wrenches the operating force, F, shall be applied to the centre of the hand hold position of the grip
or of the marked load point and shall be at 90° to the axis of the tool within +/- 5° angular deviation.
For torque screwdrivers the axis of the tool shall be held parallel within +/- 5° of the axis of the
measurement device.
Tools with flexible head shall be loaded with the tool handle perpendicular to the axis of the output drive.
Where the output drive is not permanently attached, the dimensions of the drive that affect the radial
distance shall be recorded.
During measurement, analogue scales or dials shall be read in a perpendicular direction in order to minimize
parallax errors.
Type I torque tools shall be loaded with an increasing torque until the target torque value is indicated on the
torque tool. Slave pointers (memory indicators) shall not be used when taking the readings. Alternatively, a
Type I torque tool may be loaded with an increasing torque until the target torque value is indicated on the
torque measurement device. The calibration certificate shall indicate which method was used.
Every effort shall be made to stop loading a Type I torque tool at the target torque value. If the target is
under or over-achieved by less than 2 % or reading, the reading on both the torque tool and the torque
measurement device shall be recorded and the error of interpolation calculated, together with its associated
uncertainty according to Formula (12). Alternatively, the largest net error (need to clarify) shall be presented
as an additional element of uncertainty.
Type II torque tools shall be loaded with a slowly and steadily increasing torque until attainment of the
target torque is signalled by the torque tool.
The rate of torque increase shall be as defined in Table 2.

ISO/DIS 6789-2:2025(en)
Table 2 — Minimum time period for application of torque values
<1 N·m ≥10 N·m ≥100 N·m ≥1 000 N·m
Applied torque value <10 N·m
<100 N·m <1 000 N·m
Type I Class A, B, C, D, E
Type II Class A, B, C, G
>0,5 s
0,5 s 1 s 1,5 s 2 s
Minimum time to increase the torque
<2 s
from 80 % of target value to target
value
Type II Class D, E, F
>0,5 s
Minimum time to increase the torque
0,5 s 1 s 1,5 s 2 s
from 80 % of target value to target <2 s
value
Type II, Classes H, J, K
>0,5 s
Minimum time to increase the torque
0,5 s 1 s 1,5 s 2 s
from 80 % of target value to target <2 s
value
5.2 Torque measurement – loading sequence
5.2.1 General
Where the torque measurement device has not been continuously operating during the previous hour, it
shall be conditioned by three preloadings to the maximum torque of the torque tool in the measurement
direction. After the three preloadings, all load on the torque tool and the torque measurement system shall
be removed. Then after a waiting period of at least 5 seconds, the pointer or electronic display of the torque
measurement device shall be set to zero where such a facility exists.
Loadings should not be repeated, ignored or discarded. Each observed measurement should be recorded.
Torque tools with electronic measurement shall not be turned off during the whole measurement sequence.
Minimum (T ) and maximum (T ) torque values shall be taken from the marked values on the tool, or in
min max
the absence of such markings, from the manufacturer’s specifications.
If the torque tool operates in two directions, steps 1-5 of the measurement sequence detailed in Table 3 shall
be carried out separately for each direction
Type II torque tools shall be set to each target value starting from a lower value. If the target value is
exceeded during setting, then the tool setting shall be returned to the lower value and adjusted once more
to the target value. The time intervals between any two subsequent loadings shall be of the same or similar
duration.
Type I and Type II torque tools with scale or display shall first be measured at the lowest specified torque
value of the measurement range, then at approximately 60 % and finally at 100 % of the torque tool’s
maximum value. Tools with no scale or display shall be calibrated at the set value. Customers may specify
the range or single torque value to be used in the calibration, which then should be marked on the tool.
Optional additional calibration points may be inserted between T and T .
min max
Tools with a scale or display shall be loaded five times at each torque value. Tools with no scale or display
shall be calibrated 10 times at the set value. For Type II Class B, C, E, F, J and K, the necessary number of
loadings to complete one full rotation of the output drive should be completed.
5.2.2 Preloading sequence
The torque tool shall be preloaded three times at its pre-set or its maximum specified torque value without
recording. For torque screwdrivers, a full rotation of the tool should be completed to exercise each trigger
mechanism. There shall be no further preloading during the calibration sequence. Unless these preloads are
required by 5.2.1, they do not need to be performed on the torque measurement device. Type I tool pointers

ISO/DIS 6789-2:2025(en)
or displays shall then be set to zero in a position free of external forces if a zero feature is available. There
shall be no further preloading or zeroing of the torque tool during the calibration sequence.
After the preloading is complete, the display of the measurement device shall be set to zero without the
torque tool mounted.
5.2.3 Loading sequence
The measurement sequence in Table 3 includes the necessary steps to collect measurements both for the
reported values and to calculate the measurement uncertainty. Where insufficient statistical data exists
for the model of torque tool this sequence shall be followed. Where statistical data exists for the length
dependence of the tool, the final step may be omitted. For torque screwdrivers and T-handles, the final step
shall be omitted.
When using adaptors between the torque measurement device and the torque tool, users shall evaluate their
uncertainty component. This may require additional loading sequences.
Instructions for the treatment of measurements in each step of the sequence are detailed in 5.4.
Table 3 — Sequence for torque calibration
Step Purpose of step Uncertainty Target Number of loadings
No. component torque
value
1 Pre-loading before calibration T 3 without recording
max
2 Repeatability plus b b T 5 Measured values for:
re rep min
Type I all Classes
Reproducibility - series one
Type II Classes A,D,G,H
10 Measured value for:
Type II Classes B, C, E, F, J, K
3 Repeatability b 60 % of 5 measured values for:
re
T Type I all classes
max
Type II classes A,D,G,H
4 Repeatability b T 5 measured values for:
re max
Type I all classes
Type II classes A,D,G,H
5 Reproducibility - series two plus b T 5 readings
rep min
Eccentricity of output drive - series one
6 Eccentricity of output drive - series two b T 5 readings
od min
7 Eccentricit
...