ISO 12129-1:2024
(Main)Plain bearings — Tolerances — Part 1: Fits
Plain bearings — Tolerances — Part 1: Fits
This document specifies a system of fits applicable to metallic plain bearings used in general engineering for mean relative bearing clearances, ψm, of 0,56 ‰ up to 3,15 ‰. Other clearance ranges can be used depending upon the requirements in specific applications. This system of fits is not applicable to half-bearings and bushes which, due to their special characteristics, are not measured by diameter but by wall thickness, and which are dimensionally changed on assembly. It is not applicable to profile bore or tilting pad bearings, or to cases where specific tolerances have been established by consideration of the bearing performance at both extremes of clearance. This document is applicable preferably to bearings in rotating machines or transmissions, but it can be used similarly in other ranges of application.
Paliers lisses — Tolérances — Partie 1: Ajustements
General Information
Relations
Standards Content (Sample)
International
Standard
ISO 12129-1
Third edition
Plain bearings — Tolerances —
2024-12
Part 1:
Fits
Paliers lisses — Tolérances —
Partie 1: Ajustements
Reference number
© ISO 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 1
5 System of fits . 2
6 Mean relative bearing clearance . 2
7 Tolerance intervals . 2
7.1 Tolerance .2
7.2 Fundamental deviation .2
7.3 Number .3
7.4 Symbol . .3
8 Ranges of nominal dimensions . 3
9 Limit deviations . 3
10 Minimum and maximum clearances . 3
11 Example of shaft fit dimension indications . 3
12 Limit deviations and tolerance intervals . 3
Bibliography . 9
iii
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 123, Plain bearings, Subcommittee SC 3,
Dimensions, tolerances and construction details.
This third edition cancels and replaces the second edition (ISO 12129-1:2019), which has been technically
revised.
The main changes are as follows:
— Clause 4 “Symbols” has been added;
— Table 1 and Table 2 have been added, and the previous Table 1 and Table 2 have been renumbered Table 3
and Table 4;
— Table 3 and Table 4 have been corrected.
A list of all parts in the ISO 12129 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 has been established because it is not possible to use the ISO deviations given in ISO 286-1
and ISO 286-2 to develop clearance fits which correspond to the requirements of plain bearing engineering
for approximately uniform mean relative bearing clearances for all nominal size ranges.
v
International Standard ISO 12129-1:2024(en)
Plain bearings — Tolerances —
Part 1:
Fits
1 Scope
This document specifies a system of fits applicable to metallic plain bearings used in general engineering
for mean relative bearing clearances, ψ , of 0,56 ‰ up to 3,15 ‰. Other clearance ranges can be used
m
depending upon the requirements in specific applications.
This system of fits is not applicable to half-bearings and bushes which, due to their special characteristics,
are not measured by diameter but by wall thickness, and which are dimensionally changed on assembly.
It is not applicable to profile bore or tilting pad bearings, or to cases where specific tolerances have been
established by consideration of the bearing performance at both extremes of clearance.
This document is applicable preferably to bearings in rotating machines or transmissions, but it can be used
similarly in other ranges of application.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
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/
4 Symbols
For the purposes of this documents, the symbols and indices given in Tables 1 and 2, respectively, apply.
Table 1 — Symbols
Symbol Description Unit
C Bearing clearance µm
C* Alternative symbol for ψ ‰
D Nominal dimension mm
ψ Relative bearing clearance ‰
Table 2 — Indices
Indice Description
D Diametral
m Mean value
max Maximum value
min Minimum value
5 System of fits
The system of fits specified in this document is a normal system of fits, in which the fundamental deviation H
of the bearing bore diameter is in accordance with ISO 286-2. The tolerance interval of the shaft is correlated
to correspond to the mean relative bearing clearance, ψ .
m
6 Mean relative bearing clearance
The mean relative bearing clearance, ψ , in per thousand (‰), of a range of nominal dimensions is given by
m
Formula (1):
C
D,m
ψ = (1)
m
D
m
C + C
D,maxD,min
C = (2)
D,m
EXAMPLE For the nominal dimension range from 250 mm to 280 mm, the arithmetic mean of the range of nominal
dimensions is given by
250 +280
D = =265 mm
m
For ψ = 1,6 ‰, Table 1 and Formula (2) lead to the mean bearing diametral clearance
m
0,,466 +0382
C = ==0,424 mm 424 μm
D,m
and to the mean relative bearing clearance
0,424
ψ = = 1,6 ‰
m
7 Tolerance intervals
7.1 Tolerance
The tolerance is chosen so that, for a uniform mean relative bearing clearance, ψ , in each case from the
m
minimum to the maximum range of nominal dimensions, an approximately uniform maximum deviation
from the relative bearing clearance within a tolerance interval is not exceeded. The lower limit is dictated by
economy and methods of production.
The tolerance interval of the shaft in each case is smaller by one IT grade (basic tolerance grade in accordance
with ISO 286-1) than the tolerance interval of the correlated bearing bore.
7.2 Fundamental deviation
The fundamental deviation is determined by the mean relative bearing clearance, ψ .
m
7.3 Number
Each of the following values of ψ , in per thousand, corresponds to one tolerance interval:
m
— 0,56;
— 0,8;
— 1,12;
— 1,32;
— 1,6;
— 1,9;
— 2,24;
— 3,15.
When determining the value of ψ , it is recommended to consider the bearing material, load and speed
m
conditions, environmental temperature, and required mechanical accuracy.
7.4 Symbol
The symbol for the mean relative bearing clearance is ψ . If Greek letters are not available, the symbol C*
m
may be used instead of the Greek letter ψ.
8 Ranges of nominal dimensions
The ranges of nominal dimensions are more closely stepped than in ISO 286-2 so that the maximum deviation
from the mean relative bearing clearance, ψ , can be more closely adhered to.
m
9 Limit deviations
The limit deviations for the shafts are given in Table 3.
10 Minimum and maximum clearances
The minimum clearance, C , and maximum clearance, C , between the shaft and bearing bore,
D,min D,max
together with the limit deviations for the shaft which are required for the calculation of the plain bearings,
are given in Table 3.
The corresponding tolerance intervals of the relative bearing clearance are given in Table 4.
11 Example of shaft fit dimension indications
The shaft fit dimension 200 mm for a mean bearing clearance is: ψ = 1,12 ‰.
m
The preferred form is: ∅200 .
ψ 1,12
The alternative form where Greek letters are not available is: ∅200 .
C* 1,12
The alternative form where subscripts are not available is: ∅200 (C* 1,12) .
12 Limit deviations and tolerance intervals
Limit deviations for shafts and tolerance intervals for bearing clearance are given in Table 3 and tolerance
intervals of bearing clearance are given in Table 4.
Table 3 — Limit deviations for shafts and tolerance intervals for bearing clearance
a
Nominal Limit deviations for the shaft Maximum clearance, C , and minimum clearance, C , between the shaft and
D,max D,min
b
dimension, D the bearing bore
mm µm µm
for mean relative bearing clearance, ψ , of for mean relative bearing clearance, ψ , of
m m
up to and
over 0,56 ‰ 0,8 ‰ 1,12 ‰ 1,32 ‰ 1,6 ‰ 1,9 ‰ 2,24 ‰ 3,15 ‰ 0,56 ‰ 0,8 ‰ 1,12 ‰ 1,32 ‰ 1,6 ‰ 1,9 ‰ 2,24 ‰ 3,15 ‰
including
— −15 −23 −29 −37 −41 −51 −76 — 30 38 44 52 63 73 98
25 30
— −21 −29 −35 −43 −50 −60 −85 — 15 23 29 37 41 51 76
— −17 −27 −34 −43 −48 −59 −89 — 35 45 52 61 75 86 116
30 35
— −24 −34 −41 −50 −59 −70 −100 — 17 27 34 43 48 59 89
−12 −21 −33 −36 −47 −58 −71 −105 30 39 51 63 74 85 98 132
35 40
−19 −28 −40 −47 −58 −69 −82 −116 12 21 33 36 47 58 71 105
−14 −25 −34 −43 −55 −67 −82 −120 32 43 61 7
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.