ISO/FDIS 1938-1

ISO/TC 213/WG 6
Secretariat: BSI
Date: 2026-01-0602-04
Geometrical product specifications (GPS) — Dimensional measuring
equipment —
Part 1:
Plain limit gauges of linear size
Spécification géométrique des produits (GPS) — Équipement de mesure dimensionnel —
Partie 1: Calibres lisses à limite de taille linéaire
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ISO/DIS FDIS 1938-1:20242026(en)
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ii
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
3.1 Limits . 2
3.2 Gauge types . 3
3.3 Characteristics and function of gauges . 7
4 Abbreviated terms and symbols . 8
5 Design characteristics for gauges . 10
6 Metrological characteristics . 11
6.1 General . 11
6.2 Metrological characteristic relative to the type of limit gauge (GO gauge or NO GO gauge)12
7 Maximum permissible limits (MPL) on metrological characteristics . 19
7.1 General . 19
7.2 Values for calculation of MPL for limit gauges for internal features of size . 20
7.3 Values for calculation of MPL of limit gauges for external features of size . 23
7.4 Values for calculation of MPL of limit gauges . 26
8 Proving conformance with specification for limit gauges . 29
9 Verification of dimensional specification of a workpiece with limit gauges . 29
10 Marking . 31
Annex A (informative) General principles and application of limit gauging . 32
Annex B (informative) Description of the specific use of the various gauge types and the
associated uncertainty . 34
Annex C (informative) Relationship to the GPS matrix model . 37
Bibliography . 39

iii
ISO/DIS FDIS 1938-1:20242026(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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of 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 www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 213, Dimensional and geometrical product
specifications and verification, in collaboration with the European Committee for Standardization (CEN)
Technical Committee CEN/TC 290, Dimensional and geometrical product specification and verification, in
accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 1938-1:2015), which has been technically
revised.
The main changes are as follows:
— — revision of definitions 3.1.3, 3.1.43.1.3, 3.1.4,, and 3.2.13.2.1;;
— — updaterevision of design and metrological characteristics of GO gauge type B to K in Clause 5Clause 5
and in Tables 4Tables 4 and 55;;
— — inclusion of full form cylindrical ring, full form notch gauge and gap gauge in Table B.1Table B.1.
A list of all parts in the ISO 1938 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
This document is a geometrical product specification (GPS) standard and is to be regarded as a general GPS
standard (see ISO 14638). It influences chain links E, F and G of the size chain of standards in the general GPS
matrix. For more detailed information of the relation of this document to other standards and the GPS matrix
model, see Annex CAnnex C.
The ISO GPS matrix model given in ISO 14638 gives an overview of the ISO GPS system of which this document
is a part. The fundamental rules of ISO GPS given in ISO 8015 apply to this document and the default decision
rules given in ISO 14253--1 apply to specifications made in accordance with this document, unless otherwise
indicated.
This document deals with verification, using plain limit gauges, of linear sizes for features of size when the
dimensional specifications are required (see ISO 14405--1), for rigid workpieces.
NOTE Tables 4Tables 4 and 55 use the modifiers given in ISO 14405--1 and ISO 1101.
v
DRAFT International Standard ISO/FDIS 1938-1:2026(en)

Geometrical product specifications (GPS) — Dimensional measuring
equipment —
Part 1:
Plain limit gauges of linear size
1 Scope
This document specifies requirements for the most important metrological and design characteristics of plain
limit gauges of linear size.
This document defines the different types of plain limit gauges used to verify linear dimensional specifications
associated with linear size.
This document also defines the design characteristics and the metrological characteristics for these limit
gauges as well as the new or wear limits state maximum permissible limits (MPLs) for the new state or wear
limits state for these metrological characteristics.
In addition, this document describes the use of limit gauges. It covers linear sizes of up to 500 mm.
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 286--1:2010, Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes —
Part 1: Basis of tolerances, deviations and fits
ISO 1101, Geometrical product specifications (GPS) — Geometrical tolerancing — Tolerances of form,
orientation, location and run-out
ISO 14405--1, Geometrical product specifications (GPS) — Dimensional tolerancing — Part 1: Linear sizes
ISO 14253-1, Geometrical product specifications (GPS) — Inspection by measurement of workpieces and
measuring equipment — Part 1: Decision rules for verifying conformity or nonconformity with specifications
ISO 14253--2, Geometrical product specifications (GPS) — Inspection by measurement of workpieces and
measuring equipment — Part 2: Guidance for the estimation of uncertainty in GPS measurement, in calibration
of measuring equipment and in product verification
ISO 17450--2, Geometrical product specifications (GPS) — General concepts — Part 2: Basic tenets,
specifications, operators, uncertainties and ambiguities
ISO/IEC Guide 98--3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
ISO/DIS FDIS 1938-1:20242026(en)
ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated terms
(VIM)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 286--1, ISO 14405--1, ISO 17450--2,
ISO/IEC Guide 98--3 and ISO/IEC Guide 99 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1 Limits
3.1.1 3.1.1
maximum material limit of size
MMLS
upper limit of size or lower limit of size corresponding to the maximum material condition of feature of size
Note 1 to entry: MMLS includes the numerical value for the size and the specified association criteria.
Note 2 to entry: A number of different association criteria for size are given in ISO 14405--1 and ISO 17450-3.
3.1.2 3.1.2
least material limit of size
LMLS
upper limit of size or lower limit of size corresponding to the least material condition of feature of size
Note 1 to entry: LMLS includes the numerical value for the size and the specified association criteria.
Note 2 to entry: A number of different association criteria for size are given in ISO 14405--1 and ISO 17450-3.
3.1.3 3.1.3
upper limit of size
ULS
largest permissible size of a feature of size
Note 1 to entry: ULS is a numerical value.
[SOURCE: ISO 286--1:2010, 3.2.3.1]
3.1.4 3.1.4
lower limit of size
LLS
smallest permissible size of a feature of size
Note 1 to entry: LLS is a numerical value.
[SOURCE: ISO 286--1:2010, 3.2.3.2]
3.1.5 3.1.5
upper specification limit
USL
limit of a specification for a metrological characteristic of a gauge having the largest value
3.1.6 3.1.6
lower specification limit
LSL
limit of a specification for a metrological characteristic of a gauge having the smallest value
3.2 Gauge types
3.2.1 3.2.1
limit gauge
gauge designed and intended to verify only if workpiece characteristics are lower or upper at one of its
tolerance limits
Note 1 to entry: When a limit gauge is designed to verify an internal feature of size (a hole for example), then it can be
called internal limit gauge.
Note 2 to entry: When a limit gauge is designed to verify an external feature of size (a shaft for example), then it can be
called external limit gauge.
Note 3 to entry: General application of limit gauge is given in Annex AAnnex A.
Note 4 to entry: A limit gauge may be physical or a virtual object (simulated by a geometrical model to be compared to
the extracted integral feature of size of the workpiece).
3.2.2 3.2.2
plain limit gauge
physical limit gauge with only one or two gauge elements, each one simulating a perfect feature of size, whose
size is derived from upper or lower specification limits of the size of a feature of size
Note 1 to entry: When a plain limit gauge consists of only one element, it is qualified as simple (simple plain limit gauge:
GO plain limit gauge, see 3.3.33.3.3 or NO GO plain limit gauge, see 3.3.43.3.4).).
Note 2 to entry: When a plain limit gauge consists of two elements, it is qualified as double (double plain limit gauge: GO
and NO GO).
3.2.3 3.2.3
gauge type A
full form cylindrical plug gauge
plain limit gauge designed to simulate a cylinder as a contacting feature with an internal cylinder
Note 1 to entry: See Table 1Table 1.
Note 2 to entry: The GO gauge type A simulates a dimensional specification defining the maximum material limit of size
with the envelope requirement when the gauge length is greater or at least equal to the length of the feature of size of the
workpiece.
3.2.4 3.2.4
gauge type B
segmental cylindrical bar gauge
plain limit gauge designed to simulate two opposite angular portions of a cylinder as a contacting feature with
an internal cylinder
Note 1 to entry: See Table 1Table 1.
ISO/DIS FDIS 1938-1:20242026(en)
3.2.5 3.2.5
gauge type C
segmental cylindrical bar gauge with reduced gauging surfaces
segmental cylindrical bar gauge designed to simulate two reduced opposite angular portions of a cylinder as
a contacting surface with an internal cylinder
Note 1 to entry: See Table 1Table 1.
3.2.6 3.2.6
gauge type D
full form spherical plug gauge
plain limit gauge designed to simulate a circle as a contacting feature with an internal cylinder
Note 1 to entry: See Table 1Table 1.
Note 2 to entry: The shape of this gauge type is not spherical, but a torus -. As per tradition, the name is “spherical plug
gauge”.
3.2.7 3.2.7
gauge type E
segmental spherical plug gauge
plain limit gauge designed to simulate two opposite angular portions of a circle as a contacting feature with
an internal cylinder
Note 1 to entry: See Table 1Table 1.
Note 2 to entry: The shape of this gauge type is not spherical but a torus - per tradition the name is “segmental spherical
plug gauge”.
3.2.8 3.2.8
gauge type F
bar gauge
full form bar gauge
plain limit gauge designed to simulate two opposite planes as a contacting feature with an internal feature of
size consisting of two opposite planes
Note 1 to entry: See Table 1Table 1.
3.2.9 3.2.9
gauge type G
rod gauge with spherical ends
plain limit gauge designed to simulate two opposite points as a contacting feature with an internal feature of
size consisting of two opposite planes or of a cylinder
Note 1 to entry: See Table 1Table 1.
Note 2 to entry: The active part of a rod gauge with spherical endstype G consists only of two points: the two points at
the largest distance between the two spheres.

Table 1 — Types of limit gauge for internal feature of size
Nominal contacting feature with
feature of size of type
Limit gauge Type Illustration
Two opposite
Cylinder
parallel planes
Two opposite
Full form cylindrical plug gauge Gauge type A Cylinder parallel straight
lines
Two opposite
Two opposite
angular
Segmental cylindrical bar gauge Gauge type B parallel straight
portions of
lines
cylinder
Two opposite
angular Two opposite
Segmental cylindrical bar gauge
Gauge type C reduced parallel line
with reduced gauging surfaces
portions of segments
cylinder
Full form spherical plug gauge Gauge type D Circle Two points

ISO/DIS FDIS 1938-1:20242026(en)
Nominal contacting feature with
feature of size of type
Limit gauge Type Illustration
Two opposite
Cylinder
parallel planes
Two opposite
angular
Segmental spherical plug gauge Gauge type E Two points
portions of
circle
Two opposite
Bar gauge Gauge type F Not applicable
parallel planes
Rod gauge with spherical ends Gauge type G Two points Two points

3.2.10 3.2.10
gauge type H
full form cylindrical ring gauge
plain limit gauge designed to simulate a cylinder as contacting feature with an external cylinder
Note 1 to entry: See Table 2Table 2.
3.2.11 3.2.11
gauge type J
full form notch gauge
plain limit gauge designed to simulate straight lines or flat surfaces on two opposite parallel planes as
contacting features with an external feature of size consisting of a cylinder or two opposite planes
Note 1 to entry: See Table 2Table 2.
3.2.12 3.2.12
gauge type K
gap gauge
plain limit gauge designed to simulate portions (straight lines or flat surfaces) on two opposite planes as
contacting feature with an external feature of size consisting of a cylinder or two opposite planes
Note 1 to entry: See Table 2Table 2.
Table 2 — Types of limit gauge for external feature of size
Nominal contacting feature with
feature of size of type:
Limit gauge Type Illustration
Two opposite
Cylinder”
parallel planes”
Full form cylindrical ring gauge Gauge type H Cylinder Not applicable

Two opposite
Two opposite parallel
Full form notch gauge Gauge type J parallel straight
planes
lines
Two opposite
Two opposite parallel
Gap gauge Gauge type K parallel straight
portions of planes
line segments
3.3 Characteristics and function of gauges
3.3.1 3.3.1
non-adjustable gauge
gauge with an inherent, stable and not changeable nominal metrological characteristic
Note 1 to entry: The metrological characteristics of a non-adjustable gauge can change with, for example, temperature
and wear.
EXAMPLE A full form cylindrical plug gauge type A and a full form cylindrical ring gauge type H are non-adjustable
gauges.
3.3.2 3.3.2
adjustable gauge
gauge designed in a way that the inherent nominal metrological characteristic can be intentionally changed
by the user
Note 1 to entry: The metrological characteristics of an adjustable gauge can also change with, for example, temperature
and wear.
EXAMPLE A variable gap gauge type K and a variable rod gauge with spherical endstype G are adjustable gauges.
ISO/DIS FDIS 1938-1:20242026(en)
3.3.3 3.3.3
GO gauge
gauge designed to verify the size of the workpiece relative to maximum material size according to dimensional
specification
Note 1 to entry: Usually relative to the MMLS of the dimensional specification, the GO gauge passing over the actual
feature of size of the workpiece, defines an acceptance and the GO gauge, not passing over the actual feature of size of the
workpiece defines a non-acceptance.
3.3.4 3.3.4
NO GO gauge
gauge designed to verify the size of the workpiece relative to least material size according to dimensional
specification
Note 1 to entry: Usually relative to the LMLS of the dimensional specification, the NO GO gauge not passing over the actual
feature of size of the workpiece defines an acceptance and the NO GO gauge passing over the actual feature of size of the
workpiece defines a non-acceptance.
3.3.5 3.3.5
length of gauge element
active length of a gauge in the direction perpendicular to a cross section of the gauged feature of size
Note 1 to entry: For a cylindrical gauge element, it is the length of the cylinder (see Table 4Table 4).). For a gauge element
of type “two parallel opposite surfaces”, it is the length of the bar or notch (see Table 4Table 4).). For a gap gauge type K,
it is the width of the anvils (see Table 4Table 4).).
3.3.6 3.3.6
height of gauge element
active height of a gauge in the direction parallel to a cross section of the gauged feature of size
Note 1 to entry: For a gauge element of type two parallel opposite surfaces, it is the height of the bar or notch (see
Table 4Table 4).). For a gap gauge type K, it is the height of the anvils (see Table 4Table 4).).
3.3.7 3.3.7
new state specification
specification for metrological characteristics of a new gauge to be used by a manufacturer
or supplier
3.3.8
wear limits state specification
specification for metrological characteristics of a used gauge
Note 1 to entry: The user may use standardized wear limits state specifications, e.g. as given in this document.
Note 2 to entry: The wear limits state specifications consider the gauge as used, and can include wear limits.
4 Abbreviated terms and symbols
For the purposes of this document, the abbreviated terms and symbols given in Table 3Table 3 apply.
Table 3 — Abbreviated terms and symbols
Abbreviated term Description
B width of segmental gauge element
GO GO gauge
Abbreviated term Description
LT length of gauge element
HG height of gauge element
USL upper specification limit (of a gauge)
LG length of gauge element
LSL lower specification limit (of a gauge)
LMLS least material limit of size
M new state gauge
MMLS maximum material limit of size
MPL maximum permissible limits of a metrological characteristic
NO GO NO GO gauge
S size
SR spherical radius of the gauge
U wear limits state gauge
W workpiece
Symbol Description
F tolerance value of form specification on limit gauge
H interval tolerance on the size characteristic, S, for a limit gauge in the new state
T tolerance
y amount outside of workpiece tolerance limit taking into account a margin of wear limit for
internal feature of size
y amount outside of workpiece tolerance limit taking into account a margin of wear limit for
external feature of size
z distance between centre of tolerance for GO new state gauge and the lower specification
limit of an internal feature of size of a workpiece
z1 distance between centre of tolerance for GO new state gauge and the upper specification
limit of an external feature of size of a workpiece
α safety allowance for measurement uncertainty for internal feature of size
α safety allowance for measurement uncertainty for external feature of size
ULS, w upper limit of size of the workpiece
L lower limit of size of the workpiece
LS, w
USL a, b Upperupper specification limit in a state “a” of a gauge “b”, where “a” is “M”, for new state
and “U” for wear limits state and where “b” is “GO”, for GO gauge or “NO GO” for NO GO
gauge, e.g. U NO GO for the upper specification limit of the NO GO gauge for the wear
SL, U,
limits state
LSL,a, b Lowerlower specification limit in a state “a” of a gauge “b”, where “a” is “M”, for new state
and “U” for wear limits state and where “b” is “GO”, for GO gauge or “NO GO” for NO GO
gauge and, e.g. LSL, M, GO for the lower specification limit of the GO gauge for new state
ISO/DIS FDIS 1938-1:20242026(en)
5 Design characteristics for gauges
The length of the GO gauge type A, B and H shall be greater or at least equal to the length of the feature of size
of the workpiece with the envelope requirement, unless otherwise agreed between the user and the
manufacturer.
The height and length of the GO gauge type F and J shall greater or at least equal to the length of the feature of
size of the workpiece with the envelope requirement, unless otherwise agreed between the user and the
manufacturer.
For rod gauges with spherical ends the contact radius of each gauging surface shall be not greater than
50 percent of the nominal size of the workpiece to be verified.
The material used for gauges shall be selected with due consideration to its size stability, durability and
stiffness.
Gauging elements shall normally be manufactured from a high quality steel suitably selected to provide a high
degree of wear resistance after heat treatment. Other wear-resistant materials, e.g. tungsten carbide, may be
used provided that their wear qualities are not less than those of the steel specified above.
NOTE The temperature expansion coefficient of the material used is to be considered together with the wear
resistance.
Hard plating or other surface treatments in order to improve the wear resistance of the surface may also be
applied to gauging surfaces, but the thickness of deposit shall at least be of an amount, that an acceptable gauge
always has a fully intact layer of wear resistant material.
The hardness of the gauging surface shall not be less than 670 HV 30 (approximately 58 HRC), irrespective of
the type of material.
There can be specific applications where the use of special materials (e.g. aluminium and glass) is required by
the nature of the workpiece or the manufacturing environment. In such cases, it is potentiallypossible not to
have the required hardness or wear resistance.
The gauging surface shall be finished by fine grinding or lapping or a process which results in a smooth type
of surface. The surface roughness of gauging surface shall be specified and the R value shall not exceed 10 %
a
of the new state gauge MPL for size (see Example and Table 6Table 6)) with an upper tolerance limit value of
0,2 µm, and nesting index (cut-off) value of 0,8 mm (see ISO 21920-1).
EXAMPLE Surface texture specification related to Ra parameter on gauging surface:

Additional surface texture parameters can be specified.
All sharp edges shall be removed unless functionally required.
The design of the grip handle of the plain limit gauge shall take into account ergonomic considerations (e.g.
knurling, hexagon shape) and the associated characteristics to the grip handle are also design characteristics.
Design options on some gauges are possible; these are given below.
— — Air slot: for a GO gauge- full form cylindrical plug gaugegauge type A: this option is intended to verify
a blind hole, to avoid phenomena of compression and suction. This option requires defining the air slot
dimensions.
— — Precentering/pilot (see Figure 1Figure 1):): for a GO gauge or a NO GO gauge - full form cylindrical
plug gauge type A and gauge and segmental cylindrical bar gaugetype B; this option is intended to facilitate
the introduction of the gauge in the workpiece. This option requires defining the precentering or pilot
dimensions.
When a gauge with precentering option is used for a blind hole, an air slot option may be used.

Figure 1 —— Example of precentering option
Other specific design characteristics, attached to a type of gauge, are described in Tables 4Tables 4 and 55.
6 Metrological characteristics
6.1 General
A plain limit gauge has one or two gauge elements (GO gauge or NO GO gauge, or GO and NO GO gauge).
Metrological characteristics are defined for these gauge elements. These metrological characteristics influence
the quality of the evaluation made using the gauge.
The common plain limit gauges are non-adjustable gauges. Adjustable gauges (NO GO or GO gauges) exist
which may be adjusted at any desired nominal value and according to the permissible wear limits.
NOTE 1 Any trespassing of the GO workpiece limit may be easily avoided by adjusting the new GO adjustable gauge
within the limits, and by adjusting it anew at the same limit as soon as wear brings its size to the size of the GO workpiece
limit with a shift of a or a1 inwards. For NO GO adjustable gauges, they may be adjusted to the size of the NO GO workpiece
limit with the shift of a or a1 inwards.
The most important metrological characteristics for the gauge elements are the size characteristic and form
characteristic. The modifiers defined in ISO 14405--1 and the symbols defined in ISO 1101 can be used to
define these metrological characteristics.
ISO/DIS FDIS 1938-1:20242026(en)
The size characteristic can be seen metrologically by different ways. For example, on a cylinder, it is possible
to evaluate the maximum inscribed diameter, the minimum circumscribed diameter, the minimum local
diameter, the maximum local diameter or the least square diameter. Each of them can yield different result of
measurement. For this reason, the metrological characteristic includes this information (by adding after the
size one or more modifiers as defined in ISO 14405--1).
Depending on the use of the plain gauge and its type, the metrological characteristic impacting the uncertainty
of verification can be different, for the same plain gauge.
NOTE 2 When a slot without envelope requirement is checked for its lower tolerance limit with a gauge type A, two
parallel lines will be checked which do not exactly correspond to the definition for two-point size. The gauge type G is the
gauge type that follows the definition for two-point size.
This document describes potential metrological characteristics available on plain limit gauge. The final
decision to select one or several metrological characteristics is left to the user.
6.2 Metrological characteristic relative to the type of limit gauge (GO gauge or NO GO
gauge)
Table 4Table 4 and Table 5Table 5 give potential metrological characteristics associated to a gauge type, but
also complementary design characteristics as defined in Clause 5Clause 5. Depending on the need of the user,
a set of these metrological characteristics shall be defined; by default, the two-point size is required for the
size characteristic, S, of the gauge limit and the form deviation also.
Table 4 — List of potential design and metrological characteristics for external gauge type
Description Complementary Metrological characteristics for
design
GO gauge NO GO gauge
characteristics
Full form cylindrical plug gauge —

Gauge type A
LG
Segmental cylindrical bar gauge —

Gauge type B
Description Complementary Metrological characteristics for
design
GO gauge NO GO gauge
characteristics
LG
B
Segmental cylindrical bar gauge with
reduced gauging surfaces — Gauge type
C
ISO/DIS FDIS 1938-1:20242026(en)
Description Complementary Metrological characteristics for
design
GO gauge NO GO gauge
characteristics
LG
B
LT
Full form spherical plug gauge — Gauge

type D
Description Complementary Metrological characteristics for
design
GO gauge NO GO gauge
characteristics
R
LT
Segmental spherical plug gauge —

Gauge type E
B
LT
R
Bar gauge — Gauge type F
ISO/DIS FDIS 1938-1:20242026(en)
Description Complementary Metrological characteristics for
design
GO gauge NO GO gauge
characteristics
LG
HG
Rod gauge with spherical ends — Gauge

type G
SR
a
Default metrological characteristics which shall be considered.
The modifier defines the minimum circumscribed size(see ISO 14405-1).
The modifier defines the two-point size (see ISO 14405-1).
The modifier ACS  defines the size characteristics in any cross section (see ISO 14405-1).
Description Complementary Metrological characteristics for
design
GO gauge NO GO gauge
characteristics
The modifier UF  defines an united feature, defined from more than one geometrical feature (see ISO 14405-1).
Table 5 — List of potential design and metrological characteristics for internal gauge type
Description Complementary Metrological characteristics for
design
GO gauge NO GO gauge
characteristics
Full form cylindrical ring gauge — Gauge type H
Dy
LG
Full form notch gauge — Gauge type J LG
ISO/DIS FDIS 1938-1:20242026(en)
Description Complementary Metrological characteristics for
design
GO gauge NO GO gauge
characteristics
HG
Gap gauge — Gauge type K LG
Description Complementary Metrological characteristics for
design
GO gauge NO GO gauge
characteristics
HG
ISO 10579-NR – Restrained condition:
a)  normally the dimension HG is vertical compared to
the gravity direction
b)  gap gaugesGauge type Ks shall only be used for rigid
workpieces
a
defaultDefault metrological characteristics which shall be considered.
The modifier defines the maximum inscribed size(see ISO 14405--1).
The modifier defines the two-point size (see ISO 14405-1).
The modifier ACS  defines the size characteristics in any cross section (see ISO 14405--1).
7 Maximum permissible limits (MPL) on metrological characteristics
7.1 General
The MPLs for a gauge are completely equivalent to the specification limits on a characteristic.
a) a) The MPLs on form and orientation characteristics are asymmetrical.
ISO/DIS FDIS 1938-1:20242026(en)
1) 1) The upper tolerance limit of MPL on these characteristics is equal to the value of F given in
Table 6Table 6 and depending on the type of the gauge.
2) 2) The lower tolerance limit of MPL on these characteristics is equal to 0.
3) 3) The evaluation of these characteristics shall be in accordance with ISO 1101 and shall fulfil
MPLs.
EXAMPLE 1 A metrological characteristic of cylindricity with its MPLs is equivalent to the following requirement:
. . Its meaning is given in ISO 1101.
b) b) Specifications for metrological characteristics associated to the size characteristic to a limit
gauge of the same type used as a GO gauge and as a NO GO gauge are different (see 7.27.2 and 7.37.3)) and
applicable by default to the two-point size, S . .
Specifications of the gauges for new or wear limits state attached to the size metrological characteristics
associated to these tolerance limits are always different for GO gauges and may be equal for NO GO gauges.
The new state specification limits of GO gauges are always positioned inside the workpiece tolerance limits.
Tables 6Tables 6 to 1111 can be used directly when the tolerance of the dimension of feature of size of
workpiece is given as a code according to ISO 286--1. When the size tolerance is not given as an ISO code, the
standard tolerance grade shall be defined as the standard tolerance grade corresponding to the first tolerance
interval, T, given in Tables 7Tables 7 to 1111,, lower than the tolerance interval of the workpiece in the same
range of nominal sizes.
EXAMPLE 2 For a dimensional specification given on the workpiece, by 20 ± 0,02 , , the tolerance interval on the
workpiece is equal to 40 µm. In Table 8Table 8,, in the nominal range in which 20 is included, the lower standardized
tolerance interval is equal to 33 µm, corresponding to the standard tolerance grade equal to 8, which is to be used to
define the metrological characteristic for a plain limit gauge to verify this dimensional specification.
NOTE For GO gauges, the specification limits are positioned by z and z1 relative to the tolerance limit of the
workpiece (see Figures 2Figures 2 and 33)) in order to allow a certain wear and therefore a certain time in use before
the size and form is worn outside the specification for the limit gauge.
7.2 Values for calculation of MPL for limit gauges for internal features of size
The tolerances limits, defining the MPL for the size characteristic, of a GO gauge and NO GO gauge in a new
state, and in wear state for internal features of size in relation to workpiece tolerance limits are shown in
Figure 2Figure 2.
The NO GO gauge specification is positioned relative to the LMLS of the workpiece tolerance limits.
The GO gauge specification is positioned relative to the MMLS of the workpiece tolerance limits.
ISO/DIS FDIS 1938-1:20242026(en)

Key
X : Nominal nominal value of the size workpiece
L : lower specification limit of the workpiece size
SL, W
U : upper specification limit of the workpiece size
SL, W
a
upperUpper specification limit of GO gauge for new state and for wear limits state (USL, M, GO or USL, U, GO)).
b
lowerLower specification limit of GO gauge for new state (LSL, M, GO)).
c
lowerLower specification limit of GO gauge for wear limits state (L )).
SL, U, GO
d
upperUpper specification limit of NO GO gauge for new state and for wear limits state (U or U )).
S, LM, NO GO SL, U, NO GO
e
lowerLower specification limit of NO GO gauge for new state and for wear limits state (LSL, M, NO GO or LSL, U, NO GO)).
Figure 2 —— MPL size position for GO and NO GO gauges for workpieces of internal feature of size
The value for H (see Figure 2Figure 2)) is specific for each type of limit gauge, workpiece tolerance grade and
workpiece feature size and shall be taken from Table 6Table 6.
The values of z, α and y (see Figure 2Figure 2)) is specific for each workpiece tolerance grade and workpiece
feature size, and shall be taken from Tables 7Tables 7 to 1111.
When a plug gauge is used as a NO GO limit gauge (for LMLS) of a workpiece feature (LMLS ) the requirement
W
on the size, S, of the gauge element shall be in accordance with the following gauge tolerances for new and
wear limits state (see Figure 2Figure 2):):
𝑈𝑈 𝑈𝑈 =𝑈𝑈 𝑈𝑈
SL,  U,  NO GO SL,U,NO GO SL,  M,  NO GO SL,M,NO GO
— for the upper specification limit: 𝐻𝐻
=𝑈𝑈 𝑈𝑈 −𝛼𝛼 +
SL,  w SL,w
𝐿𝐿 𝐿𝐿 =𝐿𝐿 𝐿𝐿
SL,  U,  NO GO SL,U,NO GO SL,  M,  NO GO SL,M,NO GO
𝐻𝐻
— for the lower specification limit:
=𝑈𝑈 𝑈𝑈 −𝛼𝛼−
SL,  w SL,w
where α is equal to zero when the nominal value is up to or equal to 180 mm.
When a plug gauge is used as a GO gauge (for MMLS) of a workpiece feature (MMLS ), the requirement on the
w
size, S, of the gauge element shall be in accordance with the following gauge tolerances:
a) for the new state (see Figure 2Figure 2):):
𝐻𝐻
1) for the upper specification limit:
𝑈𝑈 𝑈𝑈 =𝐿𝐿 𝐿𝐿 +𝑧𝑧 +
SL,  M,  GO SL,M,GO SL,  w SL,w
𝐻𝐻
2) for the lower specification limit:
𝐿𝐿 𝐿𝐿 =𝐿𝐿 𝐿𝐿 +𝑧𝑧−
SL,  M,  GO SL,M,GO SL,  w SL,w
b) for the wear limits state (see Figure 2Figure 2):):
𝐻𝐻
1) for the upper specification limit:
𝑈𝑈 𝑈𝑈 =𝐿𝐿 𝐿𝐿 +𝑧𝑧 +
SL,  U,  GO SL,U,GO SL,  w SL,w
2) for the lower specification limit: 𝑈𝑈 𝑈𝑈 =𝐿𝐿 𝐿𝐿 +𝛼𝛼−𝑦𝑦
SL,  U,  GO SL,U,GO SL,  w SL,w
where
y represents an amount outside of workpiece tolerance limits taking into account a margin of wear
limits of GO gauge;
α represents a safety allowance for measurement uncertainty.
7.3 Values for calculation of MPL of limit gauges for external features of size
The tolerances limits, defining the MPL for the size characteristic, of a GO gauge and NO GO gauge in a new
state, and in wear state for external features of size in relation to workpiece tolerance limits are shown in
Figure 3Figure 3.
The GO gauge specification is positioned relative to the MMLS of the workpiece tolerance.
The NO GO gauge specification is positioned relative to the LMLS of the workpiece tolerance.

ISO/DIS FDIS 1938-1:20242026(en)

Key
X : nominal value of the size workpiece
LSL, W : lower specification limit of the workpiece size
USL,W : upper specification limit of the workpiece size
a
upperUpper specification limit of GO gauge for new state (USL, M, G)).
b
lowerLower specification limit of GO gauge for new state or for wear limits state (L or L )).
SL, M, GO SL, U, GO
c
upperUpper specification limit of GO gauge for wear limits state (U )).
SL, U, GO
d
upperUpper specification limit of NO GO gauge for new state or for wear limits state (USL, M, NO GO or USL, U, NO GO)).
e
lowerLower specification limit of NO GO gauge for new state or for wear limits state (LSL, M, NO GO or LSL, U, NO GO)).
Figure 3 —— MPL size position for GO and NO GO gauges for workpieces for an external feature of
size
The value for H (see Figure 3Figure 3)) is specific for each type of limit gauge, for workpiece tolerance grade
and size and s
...