SIST EN 60191-1:2008

Mechanical standardization of semiconductor devices -- Part 1: General rules for the preparation of outline drawings of discrete devices

This part of IEC 60191 gives guidelines on the preparation of outline drawings of discrete devices. The primary object of these drawings is to indicate the space which should be allowed for devices in an equipment, together with other dimensional characteristics required to ensure mechanical interchangeability. It should be noted that complete interchangeability involves other considerations such as the electrical and thermal characteristics of the semiconductor devices concerned. The international standardization represented by these drawings therefore encourages the manufacturers of devices to comply with the tolerances shown on the drawings in order to extend their range of customers internationally. It also gives equipment designers an assurance of mechanical interchangeability between the devices obtained from suppliers in different countries, provided they allow the space in their equipment that is indicated by the drawings and take note of the more precise information on bases, studs, etc.

Mechanische Normung von Halbleiterbauelementen -- Teil 1: Allgemeine Regeln für die Erstellung von Gehäusezeichnungen von Einzelhalbleiterbauelementen

Normalisation mécanique des dispositifs à semi-conducteurs. - Partie 1: Règles générales pour la préparation du dessin des boîtiers des dispositifs à semi-conducteurs

La CEI 60191-1:2007 donne des lignes directrices pour la préparation des dessins d'encombrement des dispositifs discrets. Il convient également de se référer à la CEI 60191-6 pour la préparation des dessins d'encombrement des dispositifs discrets pour montage en surface. Les principales modifications par rapport à l'édition précédente sont les suivantes:
- exigence ajoutée relative aux dimensions SI pour de nouveaux dessins à publier;
- les anciennes règles concernant les dimensions en pouces sont indiquées dans une annexe informative;
- les anciennes règles relatives à la codification sont indiquées dans une annexe informative;
- incorporation des suppléments;
- mise à jour des références et
- restructuration et nouvelle numérotation.

Mehanska standardizacija polprevodniških elementov - 1. del: Splošna pravila za pripravo tehničnih risb diskretnih elementov (IEC 60191-1:2007)

General Information

• Status: Withdrawn
• Publication Date: 07-Nov-2007
• Withdrawal Date: 15-Apr-2021
• ICS: 01.100.25 - Electrical and electronics engineering drawings
• ICS: 31.080.01 - Semiconductor devices in general
• ICS: 31.240 - Mechanical structures for electronic equipment
• Technical Committee: I11 - Imaginarni 11
• Current Stage: 9900 - Withdrawal (Adopted Project)
• Start Date: 09-Apr-2021
• Due Date: 02-May-2021
• Completion Date: 16-Apr-2021
• Ref Project: EN 60191-1:2007 - Mechanical standardization of semiconductor devices - Part 1: General rules for the preparation of outline drawings of discrete devices

Relations

• Replaced By: SIST EN IEC 60191-1:2018 - Mechanical standardization of semiconductor devices - Part 1: General rules for the preparation of outline drawings of discrete devices (IEC 60191-1:2018)
• Effective Date: 03-Apr-2018
• Replaced By: SIST EN IEC 60191-1:2018 - Mechanical standardization of semiconductor devices - Part 1: General rules for the preparation of outline drawings of discrete devices (IEC 60191-1:2018)
• Effective Date: 07-Jun-2022
• Revised: SIST EN IEC 60191-1:2018 - Mechanical standardization of semiconductor devices - Part 1: General rules for the preparation of outline drawings of discrete devices (IEC 60191-1:2018)
• Effective Date: 01-Nov-2016

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN 60191-1:2008
01-januar-2008
0HKDQVNDVWDQGDUGL]DFLMDSROSUHYRGQLãNLKHOHPHQWRYGHO6SORãQDSUDYLOD]D
SULSUDYRWHKQLþQLKULVEGLVNUHWQLKHOHPHQWRY,(&
Mechanical standardization of semiconductor devices -- Part 1: General rules for the
preparation of outline drawings of discrete devices
Mechanische Normung von Halbleiterbauelementen -- Teil 1: Allgemeine Regeln für die
Erstellung von Gehäusezeichnungen von Einzelhalbleiterbauelementen
Normalisation mécanique des dispositifs à semi-conducteurs. - Partie 1: Règles
générales pour la préparation du dessin des boîtiers des dispositifs à semi-conducteurs
Ta slovenski standard je istoveten z: EN 60191-1:2007
ICS:
01.100.25 5LVEHVSRGURþMD Electrical and electronics
HOHNWURWHKQLNHLQHOHNWURQLNH engineering drawings
31.080.01 Polprevodniški elementi Semiconductor devices in
(naprave) na splošno general
31.240 Mehanske konstrukcije za Mechanical structures for
elektronsko opremo electronic equipment
SIST EN 60191-1:2008 en,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

SIST EN 60191-1:2008

---------------------- Page: 2 ----------------------

SIST EN 60191-1:2008


EUROPEAN STANDARD
EN 60191-1

NORME EUROPÉENNE
June 2007
EUROPÄISCHE NORM

ICS 31.080.01


English version


Mechanical standardization of semiconductor devices -
Part 1: General rules for the preparation
of outline drawings of discrete devices
(IEC 60191-1:2007)


Normalisation mécanique des dispositifs  Mechanische Normung
à semi-conducteurs - von Halbleiterbauelementen -
Partie 1: Règles générales Teil 1: Allgemeine Regeln
pour la préparation du dessin für die Erstellung
des boîtiers des dispositifs von Gehäusezeichnungen
à semi-conducteurs von Einzelhalbleiterbauelementen
(CEI 60191-1:2007) (IEC 60191-1:2007)




This European Standard was approved by CENELEC on 2007-05-01. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the
Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels


© 2007 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60191-1:2007 E

---------------------- Page: 3 ----------------------

SIST EN 60191-1:2008
EN 60191-1:2007 - 2 -
Foreword
The text of document 47D/678/FDIS, future edition 2 of IEC 60191-1, prepared by SC 47D, Mechanical
standardization for semiconductor devices, of IEC TC 47, Semiconductor devices, was submitted to the
IEC-CENELEC parallel vote and was approved by CENELEC as EN 60191-1 on 2007-05-01.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2008-02-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2010-05-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 60191-1:2007 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated:
IEC 60191-6 NOTE  Harmonized as EN 60191-6:2004 (not modified).
__________

---------------------- Page: 4 ----------------------

SIST EN 60191-1:2008
- 3 - EN 60191-1:2007
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application 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.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.

Publication Year Title EN/HD Year

IEC 60191-2 1966 Mechanical standardization of semiconductor - -
+ supplements devices -
+ amendments Part 2: Dimensions


1) 2)
IEC 60191-4 - Mechanical standardization of semiconductor EN 60191-4 1999
devices -
Part 4: Coding system and classification into
forms of package outlines for semiconductor
device packages


3) 1)
ISO 370 - Toleranced dimensions - Conversion from - -
inches into millimetres and vice versa




1)
Undated reference.
2)
Valid edition at date of issue.
3)
ISO 370 has been withdrawn on 2000-05-18.

---------------------- Page: 5 ----------------------

SIST EN 60191-1:2008

---------------------- Page: 6 ----------------------

SIST EN 60191-1:2008


INTERNATIONAL IEC


STANDARD 60191-1





Second edition
2007-04


Mechanical standardization of semiconductor
devices –
Part 1:
General rules for the preparation of outline
drawings of discrete devices


PRICE CODE
Commission Electrotechnique Internationale W
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue

---------------------- Page: 7 ----------------------

SIST EN 60191-1:2008
– 2 – 60191-1 © IEC:2007(E)
CONTENTS
FOREWORD.4

1 Scope and object.6
2 Normative references .6
3 Terms and definitions .6
4 General rules for all drawings .8
4.1 Drawing layout .8
4.2 Dimensions and tolerances .8
4.3 Methods for locating the datum .10
4.4 Numbering of terminals .10
5 Additional rules .12
5.1 Rules for device and case outline drawings .12
5.2 Rules to specify the dimensions and positions of terminals.12
5.3 Rules for gauge drawings.13
6 Inter-conversion of inch and millimetre dimensions and rules for rounding off.13
7 Rules for coding .14

Annex A (informative) Reference letter symbols.15
Annex B (normative) Standardization philosophy .18
Annex C (informative) Rules to specify the dimensions and positions of terminals on a
base drawing .23
Annex D (normative) General philosophy of flat base devices .30
Annex E (informative) Examples of semiconductor device drawing .32
Annex F (informative) Former rules for rounding off .36
Annex G (informative) Former rules for coding.38

Bibliography.39

Figure 1 – Numbering of terminals of lozenge – shaped bases.11
Figure 2 – System to indicate the dimensions of the terminals .13
Figure B.1 − Example of rigid lug device .21
Figure B.2 − Example of flexible terminal device .22
Figure C.1 – Circular base outline with no tab.27
Figure C.2 – Tolerances of terminals .27
Figure C.3 – Gauge for a circular base outline with no tab .28
Figure C.4 – Circular base outline with tab.29
Figure C.5 – Gauge for a circular base outline with tab .29
Figure D.1 − Example of flat base outline.31
Figure E.1 − Long form package .32
Figure E.2 − 3 types of post/stud mount packages .32
Figure E.3 − 2 types of cylindric packages .33
Figure E.4 − Oval package, terminals in line .34

---------------------- Page: 8 ----------------------

SIST EN 60191-1:2008
60191-1 © IEC:2007(E) – 3 –
Figure E.5 − Cylindric package with different terminations .34
Figure E.6 − Flange mount package.34
Figure E.7 − Disk button package with 3 terminations .35
Figure E.8 − Special shape for bolt-fixture .35

Table A.1 – Dimensions of reference letter symbols.15

---------------------- Page: 9 ----------------------

SIST EN 60191-1:2008
– 4 – 60191-1 © IEC:2007(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

MECHANICAL STANDARDIZATION OF SEMICONDUCTOR DEVICES –

Part 1: General rules for the preparation of outline drawings
of discrete devices


FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60191-1 has been prepared by subcommittee 47D: Mechanical
standardization for semiconductor devices, of IEC technical committee 47: Semiconductor
devices.
This second edition cancels and replaces the first edition published in 1966 together with
supplements 60191-1A:1969, 60191-1B:1970 and 60191-1C:1974 and constitutes a technical
revision. The main changes from the previous edition are as follows:
– requirement added for SI-dimensions for new drawings to be published;
– former rules concerning inch-dimensions are given in an informative annex;
– former rules for coding are given in an informative annex;
– incorporation of the supplements;
– updating of references;
– restructuring and renumbering.

---------------------- Page: 10 ----------------------

SIST EN 60191-1:2008
60191-1 © IEC:2007(E) – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
47D/678/FDIS 47D/682/RVD

Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The IEC 60191 series, published under the general title Mechanical standardization of
semiconductor devices, comprises the following parts:
Part 1: General rules for the preparation of outline drawings of discrete devices
Part 2: Dimensions
Part 3: General rules for the preparation of outline drawings of integrated circuits
Part 4: Coding system and classification into forms of package outlines for semiconductor
device packages
Part 5: Recommendations applying to integrated circuit packages using tape automated
bonding (TAB)
Part 6: General rules for the preparation of outline drawings of surface mounted
semiconductor device packages
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

---------------------- Page: 11 ----------------------

SIST EN 60191-1:2008
– 6 – 60191-1 © IEC:2007(E)
MECHANICAL STANDARDIZATION OF SEMICONDUCTOR DEVICES –

Part 1: General rules for the preparation of outline drawings
of discrete devices



1 Scope and object
This part of IEC 60191 gives guidelines on the preparation of outline drawings of discrete
devices.
NOTE For preparation of outline drawings of surface mounted discrete devices, IEC 60191-6 should be referred to
as well.
The primary object of these drawings is to indicate the space which should be allowed for
devices in an equipment, together with other dimensional characteristics required to ensure
mechanical interchangeability.
It should be noted that complete interchangeability involves other considerations such as the
electrical and thermal characteristics of the semiconductor devices concerned.
The international standardization represented by these drawings therefore encourages the
manufacturers of devices to comply with the tolerances shown on the drawings in order to
extend their range of customers internationally. It also gives equipment designers an
assurance of mechanical interchangeability between the devices obtained from suppliers in
different countries, provided they allow the space in their equipment that is indicated by the
drawings and take note of the more precise information on bases, studs, etc.
NOTE Additional details on the standardization philosophy used in this standard are given in Annex B.
2 Normative references
The following referenced documents are indispensable for the application 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.
IEC 60191-2:1966, Mechanical standardization of semiconductor devices – Part 2:
Dimensions (including all supplements and amendments)
IEC 60191-4, Mechanical standardization of semiconductor devices – Part 4: Coding system
and classification into forms of package outlines for semiconductor device packages
ISO 370, Toleranced dimensions – Conversion from inches to millimetres and vice versa
(withdrawn 2000-05)
3 Terms and definitions
For the purposes of this document, the following definitions apply.
3.1
device outline drawing
drawing which includes all dimensional characteristics required for the mechanical
interchangeability of the complete device. It includes the case or body, all terminals and the
locating tab if present

---------------------- Page: 12 ----------------------

SIST EN 60191-1:2008
60191-1 © IEC:2007(E) – 7 –
3.2
terminal
that part of the semiconductor device primarily used in making an electrical, mechanical or
thermal connection. Examples of terminals are flexible leads, rigid leads, pins, studs, etc.
3.3
case outline drawing
drawing which includes all dimensional characteristics required for the mechanical
interchangeability of the case or body. It does not include the dimensions of the terminals or
the locating tab if present, but their positions are shown by dotted lines
3.4
base drawing
drawing which includes all dimensional characteristics required for the mechanical
interchangeability of the terminals and mechanical index
NOTE 1 Examples of these characteristics are: lead length, lead diameters with controlled zones, lead spacing,
pitch circle diameter, thickness, width and length of a tab, etc
NOTE 2 The diameter or major axis of the case outline should not be given on the base drawing.
NOTE 3 Many semiconductor devices have identical cases, but differ in the number or the length of terminals. It is
also possible to have the same type of base associated with cases which are not identical.
Consequently, there are advantages in having:
a) a single drawing including only the dimensional characteristics of the case outline and separate drawings for
the various bases which can be associated with this case outline,
or
b) a single drawing including only the dimensional characteristics of the base and separate drawings for the
various case outlines which can be associated with this base.
3.5
mechanical index
locating feature, or that portion of the device specifically designed to provide orientation.
NOTE Examples of a mechanical index are: key, keyway, locating tab, etc.
3.6
visual index
any single terminal (or omission of) readily distinguished by the eye from others or any
distinctive boss, stippled pattern or colour mark adjacent to a terminal
3.7
datum
a theoretically exact geometric reference (such as axes, planes, straight lines etc.) to which
toleranced features are related. Datums may be based on one or more datum features of a
part
[ISO 5459:1981, definition 3.1]
3.8
seating plane or seating base
reference plane from which, in general, outline and base dimensions are given
3.9
seated height or mounted height
distance from the seating plane to the top of any exposed tip or rigid terminal present,
otherwise to the top of the outline. Flexible terminals should not be included as part of the
seated height, but the mounted height should include a minimum allowance necessary for an
axially mounted flexible lead to be bent at right angles

---------------------- Page: 13 ----------------------

SIST EN 60191-1:2008
– 8 – 60191-1 © IEC:2007(E)
3.10
controlled cylindrical zone
zone which defines a portion of the body of minimum length over which the diameter is
controlled to closer tolerances than is allowed over the full length of the body
4 General rules for all drawings
NOTE General rules for the preparation of outline drawings of surface mounted semiconductor device packages
are given in IEC 60191-6.
4.1 Drawing layout
General rules for the drawing layout are as follows.
a) A drawing should show all dimensions required to ensure mechanical interchangeability.
b) The drawing using third angle projection, should include:
– a suitable side-view;
– suitable end-views, where appropriate;
– such additional views and details as are required to show any special configuration or
features.
c) The following information should be put in the cartouche, at the bottom of the page:
– the projection method where there is more than one view, indicated as follows:

– date of publication of the drawing;
– IEC code number;
– country of origin and code of that country indicated by sign Δ;
NOTE This is no longer in practice.
– other interested countries and codes of those countries.
d) When a drawing is re-issued because of modifications, the changes made should be
indicated by arrows in the margin. The date of publication of the revised issue and of the
superseded issue should be stated.
e) While drawings need not to be drawn to scale, they should be roughly in proportion and,
where necessary for clarity, enlarged detail drawing(s) should be used.
4.2 Dimensions and tolerances
Application of dimensions and tolerances are as follows.
a) Dimensions of bases, outlines, etc. quoted shall apply to the finished product. They
should, therefore, not quote manufacturing tolerances, but give customers acceptance
limits.

---------------------- Page: 14 ----------------------

SIST EN 60191-1:2008
60191-1 © IEC:2007(E) – 9 –
b) The following types of dimension may be used on the drawings as appropriate:
i) Toleranced dimensions
A toleranced dimension can be expressed:
– preferably by both minimum and maximum limits
(example: L = 5,77 mm, L = 5,82 mm); or
min max
– by a nominal value and maximum and minimum limits. Such a nominal value
need not necessarily be the average of two limits
+0,4
(example: L =6mm ).
−0,2
ii) Untoleranced dimensions
– Untoleranced limiting dimensions
i.e.: minimum only or maximum only
(example: L = 5,85 mm) .
max
– Untoleranced nominal dimensions
These dimensions may be used:
– either for general information as an actual nominal figure;
– or to specify true geometrical position (by means of linear or angular
dimensions). Such dimensions shall be indicated by an asterisk (*) after
the numerical value, the asterisk in this sense meaning "true geometrical
position"
(example: L = 5,85 mm).
nom
c) Single minimum, single maximum or single nominal (where not given for general
information) dimensions should be stated in decimals to such a number of places as is
considered adequate to express the degree of accuracy appropriate for that dimension;
e.g. if measurement to the nearest 0,001 mm is considered appropriate, the dimension
should be expressed to the third decimal place (for example 0,500 mm), but if the
measurement to the nearest 0,01 mm is sufficient, the dimension should be expressed to
the second decimal place (for example 0,50 mm) and so on. Similar consideration should
be given to the number of decimal places necessary when an original dimension is
expressed in millimetres.
d) Limiting values or nominal value and limits of a toleranced dimension should be stated
with the same number of decimal places (e.g. 0,016 mm min. – 0,017 mm nom. –
0,019 mm max.).
e) The use of fractional mm dimensions is permitted to describe nominal hexagon sizes.
f) Numerical dimensions should not be shown directly on the figure(s). They should be
shown in tabular form under the figure(s) and correspond to the reference letter symbols
on the figure(s). The letter symbols on the figure(s) should be upright. Upper case letters
should be used for device outline and case outline dimensions and lower case letters for
base dimensions. If confusion could arise, upper case letters should preferably be used
throughout.
g) In the case of a diameter, the symbol “Ø” should appear in front of the reference letter
concerned both on the figure(s) and in the table. In cases where the cross-section is
uncontrolled (not necessarily round), the “Ø” symbol should not be used.
h) The table shall give dimensions in millimetres. The basic dimensions and system
(millimetres or inches) will be indicated immediately above the table.
NOTE Outline drawings published in IEC 60191-2 before this document came into effect may give
dimensions in inches.
i) The dimensions and limits which should normally be given and their corresponding
reference letter symbols are contained in Annex A. Some examples of drawings prepared
in accordance with these rules are given in Annex E.
Where a particular reference letter is to be used for more than one dimension on the same
drawing, use should be made of a suffix to identify the dimensions.

---------------------- Page: 15 ----------------------

SIST EN 60191-1:2008
– 10 – 60191-1 © IEC:2007(E)
Annex A cannot be expected to include all dimensions likely to be necessary for
mechanical standardization, more particularly in the future. A distinction has been made
between primary and secondary reference letter symbols, primary reference letter symbols
being those which are used most frequently, secondary reference letter symbols being
those which are used less frequently and which can, if necessary, be associated with
dimensions other than those given in the table.
j) Where it is self-evident that several angles are equal, it is not necessary to show more
than one angle on the figure(s).
k) Notes will be numbered and placed under the table of dimensions, which will have a
“notes”' column on the right-hand side. The note reference will be placed opposite the
dimension to which the note refers in the table or, when this dimension does not appear in
the table, on the figure(s). The numerical sequence of the notes should follow the
alphabetical sequence of the dimensional reference letters to which the notes refer. Notes
referring to the figure(s) should follow notes referring to dimensions given in the table.
4.3 Methods for locating the datum
These methods are listed below in order of preference. When more than one of these
methods is possible for a given device, the method appearing earliest in the list should be
used. When none of the following methods is possible, the method best suited to the device
should be used.
The datum is
a) the radial line through the centre of the mechanical or visual index;
b) the radial line midway between the two terminals which obviously comprise a gap in an
otherwise equally spaced circular terminal array;
c) the radial line 180° from the locating radius of the most isolated terminal;
d) the ra
...