AS 1275—1985
Australian Standard
METRIC SCREW THREADS FOR
FASTENERS
This Australian standard was prepared by Committee ME/28, Screw Threads. It was
approved on behalf of the Council of the Standards Association of Australia on
8 November 1984 and published on 4 April 1985.
The following interests are represented on Committee ME/28:
Confederation of Australian Industry
CSIRO, Division of Applied Physics
Department of Defence
Department of Defence Support
Department of Technical and Further Education, N.S.W.
Electricity Supply Association of Australia
Fasteners Institute of Australia
Federal Chamber of Automotive Industries
Institution of Engineers Australia
Institution of Production Engineers
Metal Trades Industry Association of Australia
Railways of Australia Committee
Society of Automotive Engineers, Australasia
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This Standard was issued in draft form for comment as DR 83215.
AS 1275—1985
Australian Standard
METRIC SCREW THREADS FOR
FASTENERS
First publi shed (as AS B275) . . . . . . . . . . . . . . 1968
AS 1275 fi rst published . . . . . . . . . . . . . . . . . . 1972
Second editi on . . . . . . . . . . . . . . . . . . . . . . . . 1985
Incorporating:
Amdt 1—1986
PUBLISHED BY STANDARDS AUSTRALIA
(STANDARDS ASSOCIATION OF AUSTRALIA)
1 THE CRESCENT, HOMEBUSH, NSW 2140
ISBN 0 7262 3628 4
AS 1275—1985
2
PREFACE
This edition of this standard was prepared by the Association’s Committee on Screw Threads, to
supersede AS 1275—1972.
Since AS 1275 was first published, the major ISO standards dealing with metric screw threads (see
later listing) have been revised, and are now in conflict with the information given in
AS 1275—1972. This is particularly true with respect to the root curvature for external threads, and
the limits specified for the thread roots of both external and internal threads.
A further important consideration is that the ISO standards for metric screw threads are now being
adopted virtually unchanged by most developed and developing countries, and therefore it is
important that the Australian standards be aligned with their ISO counterparts as much as possible.
This has been the aim in this edition of the standard.
During the preparation of AS 1275 in the early 1970s, it was noted by the committee that the ISO
symbols used for the various screw thread parameters were illogical, and so a more logical system
was introduced in the Australian standards. This was supported by sustained comment to ISO/TC1
proposing the Australian symbols. Unfortunately the Australian proposals were not accepted by
ISO/TC1 and the original ISO symbols were retained. One of the major changes in this edition
therefore has been to introduce the ISO symbology for the screw thread parameters.
The other major change is with regard to the limits given for the thread roots on both external and
internal threads. In AS 1275—1972 these limits were completely specified, whereas in the ISO
standards only the minimum minor diameter is specified for external threads and the nominal (basic)
major diameter is given for internal threads; the actual limits being indirectly controlled by the
length of straight flanks. Furthermore a root curvature for external threads is only specified for
threads intended for fasteners of property Class 8.8 and above. All other external threads may have
a root configuration in accordance with the basic/design profile.
It was considered that the ISO approach on the limits for the thread roots was practical and should
be adopted, because this would permit maximum flexibility in manufacture without being unduly
detrimental to either the strength of the screw thread or to its assembly properties. However, the ISO
root curvature for external threads, taken to the extreme could cause problems by introducing a
notch effect, which may lead to fatigue failure in threads in some steels which have a high tensile
level and/or have been severely cold worked. A cautionary statement to this effect has therefore
been included in this standard.
This standard has been based on and is in complete alignment with the following ISO standards:
ISO 68—1973
ISO General Purpose Screw Threads—Basic Profile
ISO 261—1973
ISO General Purpose Metric Screw Threads —General Plan
ISO 262—1973
ISO General Purpose Metric Screw Threads —Selected Sizes for Screws, Bolts
and Nuts
ISO 724—1978
ISO Metric Screw Threads—Basic Dimensions
ISO 965/1—1980 ISO General Purpose Metric Screw Threads —Tolerances—
Part 1: Principles and Basic Data
ISO 965/2—1980 ISO General Purpose Metric Screw Threads—Tolerances—
Part 2: Limits of Sizes for General Purpose Bolt and Nut Threads—Medium
Quality
ISO 965/3—1980 ISO General Purpose Metric Screw Threads —Tolerances—
Part 3: Deviations for Constructional Threads
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3
AS 1275—1985
CONTENTS
Page
SECTION 1. SCOPE AND GENERAL
1.1
1.2
1.3
1.4
1.5
1.6
1.7
Scope . . . . . . . . . . . . . . . .
Application . . . . . . . . . . . .
Referenced Documents . . .
Definitions . . . . . . . . . . . .
Symbols . . . . . . . . . . . . . .
Verification . . . . . . . . . . .
Stress Area (As) . . . . . . . .
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SECTION 3. DIMENSIONS AND TOLERANCES
3.1 Scope of Section . . . . . . . . . . . . . . . . . .
3.2 Basic Dimensions . . . . . . . . . . . . . . . . .
3.3 Tolerance Positions . . . . . . . . . . . . . . . .
3.4 Fundamental Deviations . . . . . . . . . . . . .
3.5 Tolerance Grades . . . . . . . . . . . . . . . . .
3.6 Tolerance Classes . . . . . . . . . . . . . . . . .
3.7 Limits of Size . . . . . . . . . . . . . . . . . . . .
3.8 Coated Threads . . . . . . . . . . . . . . . . . . .
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SECTION 4. DESIGNATION OF SCREW THREADS
4.1 Scope of Section . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 Complete Designation for Internal Threads . . . . . . . . .
4.3 Complete Designation for External Threads . . . . . . . . .
4.4 Shortened Designation for Coarse Pitch Series Threads .
4.5 Designation of a Thread Fit . . . . . . . . . . . . . . . . . . . .
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APPENDICES
A
Notes on the Production of External Threads . . . . . . . . . . . . . . .
B
Comparison of Symbols (Notations) for Screw Thread Parameters
16
17
SECTION 2. SCREW THREAD PROFILES
2.1
2.2
2.3
2.4
2.5
2.6
Scope of Section . . . . . . . .
Basic Profile . . . . . . . . . . .
Maximum Material Profile .
Least Material Profile . . . .
Limiting Profiles . . . . . . . .
Root Contours . . . . . . . . .
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AS 1275—1985
4
STANDARDS ASSOCIATION OF AUSTRALIA
Australian Standard
for
METRIC SCREW THREADS FOR FASTENERS
SECTION 1. SCOPE AND GENERAL
1.1 SCOPE. This standard specifies requirements
for single start, parallel, coarse pitch series metric
screw threads, mainly intended for threaded fasteners.
The standard covers screw threads from 1.6 mm
diameter up to and including 64 mm diameter, in
tolerance classes 6e, 6f, 6g and 8g, for external
threads; and 6H and 6G for internal threads.
The standard gives information on symbols for screw
thread parameters, tolerances, deviations, thread
classes, designation and verification.
Appendices are included giving notes on the
production of screw threads and a comparison of
symbols used in this standard and the 1972 edition.
NOTES:
1. The coarse pit ch series given in this standard comprises the
1st and 2nd choice diameter/pit ch combinations (f or coarse
pitch series threads) extracted fr om AS 1721. They are the
same as those given in ISO 261 and ISO 262; the latter
coveri ng diameters up to and including 39 mm only.
2. For informati on on the bases of the metri c screw thread
system and associated formulas, see AS 1721.
1.2
APPLICATION.
This standard gives
information on the design, manufacture and use of
ISO coarse pitch series metric parallel screw threads.
The standard is intended for adoption by industry and
government authorities concerned with the design,
manufacture and/or use of metric screw threads.
1.3 REFERENCED DOCUMENTS. The following
standards are referred to in this standard:
AS 1014
Gauging of Metric Screw Threads
AS 1098
Roller-type Screw Calliper Gauges
AS 1110
ISO Metric Hexagon Precision Bolts and
Screws
AS 1111
ISO Metric Hexagon Commercial Bolts
and Screws
AS 1112
ISO Metric Hexagon Nuts, including
Thin Nuts, Slotted Nuts and Castle Nuts
AS 1214
Hot-dip Galvanized Coatings on
Threaded Fasteners (ISO Metric Coarse
Thread Series)
AS 1252
Hi gh-strength Steel Bol ts wi th
Associated Nuts and Washers for
Structural Engineering
AS 1654
Limits and Fits for Engineering
AS 1721
General Purpose Metric Screw Threads
AS 1897
Electroplated Coatings on Threaded
Components (Metric Coarse Series)
AS XXXX* Glossary of Terms for Screw Threads
ISO 261
ISO General Purpose Metric Screw
Threads—General Plan
ISO 262
ISO General Purpose Metric Screw
Threads—Selected Sizes for Screws, Bolts
and Nuts
1.4 DEFINITIONS. For the purpose of this standard,
the definitions given in AS XXXX apply.
1.5 SYMBOLS. The symbols used in this standard to
define the screw thread parameters are given in
Table 1.1.
NOTE: These are now aligned with the ISO symbols. For
comparison of the current symbols with those used in
AS 1275—1972, see Appendix B.
TABLE 1.1
SYMBOLS
Symbol
D
D1
D2
d
d1
d2
P
H
R
S
N
L
T
TD 1
TD 2
Td
T d2
G, H
e, f, g
As
Explanation
basic major diameter of internal thread
basic minor diameter of internal thread
basic pit ch diameter of internal thread
basic major diameter of external thread
basic minor diameter of external thread
basic pit ch diameter of external thread
pitch
height of fundamental tr iangle
root radius of external thread
designation for lengths of thread engagement group
Short
designation for lengths of thread engagement group
Normal
designation for lengths of thread engagement group
Long
tolerance
tolerance on minor diameter of internal thread
tolerance on pitch diameter of external thread
tolerance on major diameter of external thread
tolerance on pitch diameter of external thread
fundamental deviations for internal threads
fundamental deviations for external threads
nominal stress area (external threads)
1.6 VERIFICATION. The form and dimensions of
screw threads to this standard should preferably be
verified by gauging in accordance with AS 1014.
The method(s) of verification (inspection) to be used on
any particular occasion will however, depend on such
things as the thread diameter, the thread class, the
number of items produced and the method of
manufacture.
Where gauging is impractical, the threads may be
verified by direct measurement or by optical methods; or
a combination of both.
1.7 STRESS AREA (A s). The cross-sectional area used
for calculating the tensile and proof loads for threaded
fasteners is based on the following formula:
NOTE: Calculated values of the stress areas are given in Table 3.3.
* In course of preparation.
COPYRIGHT
5
AS 1275—1985
SECTION 2. SCREW THREAD PROFILES
2.1 SCOPE OF SECTION. This Section specifies
the basic profile, the maximum material profiles and
the limiting profiles for external and internal metric
screw threads. The section also includes information
and values of the main elements used to derive the
basic and limiting thread profiles.
2.2 BASIC PROFILE. The basic profile of ISO
general purpose metric screw threads is shown in
Fig. 2.1. The dimensions for the various pitches are
given in Table 2.1.
NOTE: For explanati on of symbols, see Table 1.1.
Fig. 2.1. ISO BA SIC PR OFILE
TABLE 2.1
DIMENSIONS OF THE BASIC PROFILE
mill imetres
Pitch
P
0.35
0.4
0.45
0.5
0.6
0.7
0.75
0.8
1
1.25
1.5
1.75
2
2.5
3
3.5
4
4.5
5
5.5
6
H
0.303
0.346
0.389
0.433
0.519
0.606
0.649
0.692
0.866
1.082
1.299
1.515
1.732
2.165
2.598
3.031
3.464
3.897
4.330
4.763
5.196
/ H
5 8
109
410
711
013
615
218
519
820
025
532
038
544
051
063
076
089
102
114
127
140
152
0.189
0.216
0.243
0.270
0.324
0.378
0.405
0.433
0.541
0.676
0.811
0.947
1.082
1.353
1.623
1.894
2.165
2.435
2.706
2.976
3.247
443
506
570
633
760
886
949
013
266
582
899
215
532
165
798
431
063
696
329
962
595
/ H
3 8
0.113
0.129
0.146
0.162
0.194
0.227
0.243
0.259
0.324
0.405
0.487
0.568
0.649
0.811
0.974
1.136
1.299
1.461
1.623
1.786
1.948
666
904
142
380
856
332
570
808
760
949
139
329
519
899
279
658
038
418
798
177
557
COPYRIGHT
H/4
0.075
0.086
0.097
0.108
0.129
0.151
0.162
0.173
0.216
0.270
0.324
0.378
0.433
0.541
0.649
0.757
0.866
0.974
1.082
1.190
1.299
777
603
428
253
904
554
380
205
506
633
760
886
013
266
519
772
025
279
532
785
038
H/8
0.037
0.043
0.048
0.054
0.064
0.075
0.081
0.086
0.108
0.135
0.162
0.189
0.216
0.270
0.324
0.378
0.433
0.487
0.541
0.595
0.649
889
301
714
127
952
777
190
603
253
316
380
443
506
633
760
886
013
139
266
392
519
AS 1275—1985
6
2.3 MAXIMUM MATERIAL PROFILE.
2.3.1 Maximum material profile—internal thread.
The profile of an external screw thread at its
maximum material condition is shown in Fig. 2.2. It
is the same as the basic profile except that in
practice, the root is rounded as shown by the dotted
line, and cleared beyond a width P/8.
2.3.2 Maximum material profile—external thread.
The profile of an external screw thread at its maximum
material condition is shown in Fig. 2.3. It is the same as
the basic profile, except that—
(a) in practice the crests may be rounded inside the
maximum profile as shown by the dotted line; and
(b) the thread roots (minor diameter) may require to be
modified in accordance with Clause 2.6.2.
Fig. 2.2. MAX IMUM MATER IAL PR OFILE OF AN INTERN AL THR EA D
NOTES:
1.
For details of root curvature, see Clause 2.6.2 and Fig. 2.7.
2.
The actual form of any rounding of the crests or roots of the thread will not be detected by
conventi onal gauging since such gauges are cleared at the crest and root and only assess the straight
fl anks over the height of the basic profil e, i.e. 5/8 H radial depth.
3.
If assessment of the root curvature is required, verif ication by optical projection is necessary and it
is to be stated in the design requir ements.
Fig. 2.3. MAX IMUM MATER IAL PR OFILE OF AN EX TERN AL THR EA D
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7
2.4 LEAST MATERIAL PROFILE. The least
material profile of both internal and external threads
is derived from the maximum material profile using
the information given in Section 3.
2.5 LIMITING PROFILES.
2.5.1 Limiting profiles—internal threads. Typical
AS 1275—1985
limiting profiles for internal screw threads, involving
tolerance positions H and G, are shown in Figs 2.4
and 2.5 respectively.
2.5.2 Limiting profiles—external threads. Typical
limiting profiles for external screw threads, involving
tolerance positions e, f and g, are shown in Fig. 2.6.
Fig. 2.4. LIMITING PR OFILES FOR INTER NA L THR EA DS —TOLER AN CE POS ITION H
Fig. 2.5. LIMITING PR OFILES FOR INTER NA L THR EA DS —TOLER AN CE POS ITION G
COPYRIGHT
AS 1275—1985
8
Fig. 2.6. LIMITING PR OFILES FOR EXTER NA L THRE AD S—
TOLERA NC E PO SITIONS e, f AND g
2.6 ROOT CONTOURS.
2.6.1 Internal threads. The actual root contour
shall not at any point transgress the basic profile. In
practice the taps used to produce internal threads will
normally produce a rounded thread root cleared
beyond a width of P/8 as shown in Fig. 2.2.
2.6.2 External threads. The actual root contour
shall not at any point transgress the basic profile.
However it is recommended that the root profile
should not be flat, with sharp corners, but should be
smoothly rounded.
For threads on fasteners of property Class 8.8 and
higher (see AS 1110 and AS 1252) and similar
materials with similar properties, the root profile shall
have a non-reversing curvature, no portion of which
shall have a radius less than R min , which is tangential
to the thread flank. The root profile may be
comprised of arcs of minimum radius R min to which
the flanks and a flat at the root are tangential (see
Fig. 2.7). The values of R min are given in Table 2.2.
The maximum truncation is—
and the minimum truncation is—
0.125 P ≈
The above principle is recommended for all other
external threads, particularly those used in
applications subject to fatigue or impact.
External threads must be accepted by a GO screw
ring or GO screw calliper gauge.
It is not practical to specify limits for the minor
diameter of an external thread. A minimum minor
diameter can be derived when the blend radius equals
0.125 P, and the flanks are at the least material
condition, but as the flanks approach the maximum
material condition the maximum minor diameter will
tend to reduce, and the limiting values are dependent
on the actual crest diameter and pitch diameter of the
gauge as well as the subject screw thread (see
Fig. 2.7).
As noted in Fig. 2.3, conventional gauging will not
examine the root contours and it is recommended that
gauging be supplemented by profile projection of the
external thread root.
COPYRIGHT
9
AS 1275—1985
(a) Tolerance positi on h
(b) Tolerance positi ons e, f and g
Fig. 2.7. ROOT CONTOURS FOR BO LT THR EA DS
(PRO PE RTY CLASS 8.8 AN D HIGHER )
TABLE 2.2.
MINIMUM ROOT RADII
mill imetres
Pitch
P
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.6
0.7
0.75
0.8
1
1.25
1.5
1.75
2
2.5
3
3.5
4
4.5
5
5.5
6
R min
0.025
0.031
0.038
0.044
0.050
0.056
0.063
0.075
0.088
0.094
0.100
0.125
0.156
0.188
0.219
0.250
0.313
0.375
0.438
0.500
0.563
0.625
0.688
0.750
NOTE: R min = 0.125P.
COPYRIGHT
AS 1275—1985
10
SECTION 3. DIMENSIONS AND TOLERANCES
3.1 SCOPE OF SECTION. This Section sets out the
basic dimensions and thread tolerance system, and gives
information on the tolerance grades, fundamental
deviations, and tolerance classes used for ISO metric
coarse pitch series threads.
The Section also gives information on lengths of thread
engagement applicable to the tolerance classes given in
the standard.
NOTE: For further information on deviations and tolerances and
their deviation, see AS 1721.
3.2 BASIC DIMENSIONS. Values for the basic pitch
diameters and minor diameters are given in Table 3.1.
The values rounded to the third decimal place have been
calculated from the following formulas:
Basic pitch diameter
D = D - 2 × 3/8 H = D - 0.6495P
Basic pitch diameter
d2 = d - 2 × 3/8 H = D - 0.6495P
Basic minor diameter
D1 = D - 2 × 5/8 H = D - 1.0825P
Basic minor diameter
d1 = d - 2 × 5 /8 H = D - 1.0825P
3.3 TOLERANCE POSITIONS. The following
tolerance positions are given in this standard:
(a) For internal threads:
G with a positive fundamental deviation.
H with zero fundamental deviation.
See Figs 2.4 and 2.5.
(b) For external threads:
e, f and g with a negative fundamental deviation.
3.4 FUNDAMENTAL DEVIATIONS.
3.4.1
General.
Fundamental deviations are
designated by upper case letters for internal (nut)
threads, and lower case letters for external (bolt)
threads. The fundamental deviations for internal
threads and for external threads, are positioned with
respect to the basic size as shown in Fig. 3.1. For
explanation of symbols, see Table 1.1.
Fig. 3.1. SCR EW THR EA D DE VIATIONS
TABLE 3.1
BASIC DIMENSIONS
mill imetres
Basic major dia.
First Second
choice choice
1.6
1.8
2
2.2
2.5
3
3.5
4
4.5
5
6
Pitch
P
Basic
pitch
dia.
0.35
0.35
0.4
0.45
0.45
0.5
0.6
0.7
0.75
0.8
1
1.373
1.573
1.740
1.908
2.208
2.675
3.110
3.545
4.013
4.480
5.350
Basic Basic major dia.
Pitch
minor
First Second
P
dia.
choice choice
1.221
8
1.25
1.421
10
1.5
1.567
12
1.75
1.713
14
2
2.013
16
2
2.459
18
2.5
2.850
20
2.5
3.242
20
2.5
3.688
24
3
4.134
27
3
4.917
30
3.5
Basic
pitch
dia.
7.188
9.026
10.863
12.701
14.701
16.376
18.376
20.376
22.051
25.051
27.727
COPYRIGHT
Basic Basic major dia.
Pitch
minor
First Second
P
dia.
choice choice
6.647
33
3.5
8.376
36
4
10.106
39
4
11.835
42
4.5
13.835
45
4.5
15.294
48
5
17.294
52
5
19.294
56
5.5
20.752
60
5.5
23.752
64
6
26.211
Basic
pitch
dia.
Basic
minor
dia.
30.727
33.402
36.402
39.077
42.077
44.752
48.752
52.428
56.428
60.103
29.211
31.670
34.670
37.129
40.129
42.587
46.587
50.046
54.046
57.505
11
3.4.2 Internal threads. The system provides two
fundamental deviations for internal threads designated H
and G. Values for the fundamental deviations are given
in Table 3.2. The deviations are applicable to the pitch
diameter and minor diameter, and should be algebraically
added to the basic pitch diameter or basic minor
diameter as relevant.
3.4.3 External threads. The system provides three
fundamental deviations for external threads designated e,
f and g. Values for the fundamental deviations are given
in Table 3.2. The deviations are applicable to the pitch
diameter and major diameter, and should be algebraically
added to the basic pitch diameter or basic major diameter
as relevant.
3.5 TOLERANCE GRADES.
3.5.1 General. This standard covers tolerance grades 6
and 8 for external (bolt) threads and tolerance grade 6
only for internal (nut) threads. The tolerances are
applicable to the major diameter and pitch diameter, for
external threads, and the pitch diameter and minor
diameter, for internal threads. Values for the tolerance
grades are given in Table 3.2.
For information on the thread root tolerances, see
Clause 3.5.2.
3.5.2 Root diameter tolerances.
3.5.2.1 Internal threads. As indicated in Clause 2.6.1,
no specific tolerances are given for the major diameter
AS 1275—1985
of internal threads. This parameter is considered
acceptable, provided that no portion of the root curvature
transgresses the basic profile. For convenience the
minimum major diameter is given in the tabulated values
of screw thread limits (see Table 3.3).
3.5.2.2 External threads. As indicated in Clause 2.6.2,
no specific tolerances are given for the minor diameter
of external threads. This parameter is considered
acceptable, provided that the root curvature is in
agreement with Clause 2.6.2 and the minimum minor
diameter is not less than that specified for the appropriate
tolerance class in Table 3.3.
3.6 TOLERANCE CLASSES.
3.6.1 General. The method of defining a tolerance
class for ISO metric screw threads comprises two
elements, and consists of a number describing the
selected tolerance grade, followed by an upper or lower
case letter describing the selected fundamental
deviation—
e.g.
External threads: 6g 6h
Internal threads: 6H 6G.
NOTE: The tolerance class system for metric screw threads as given
in this standard is similar but in no way related to the general system
for limits and fits as given in AS 1654.
TABLE 3.2
TOLERANCES AND DEVIATIONS
Basic
major
dia.
D, d
Pitch
P
Length of
axial
engagement
N
0.35
0.35
0.4
0.45
0.45
0.5
0.6
0.7
0.75
0.8
1
1.25
1.5
1.75
2
2
2.5
2.5
2.5
3
3
3.5
3.5
4
4
4.5
4.5
5
5
5.5
5.5
6
Up
to
2.6
2.6
3
3.8
3.8
4.5
5
6
6.7
7.5
9
12
15
18
24
24
30
30
30
36
36
45
45
53
53
63
63
71
71
85
85
95
Over
1.6
1.8 *
2
2.2 *
2.5
3
3.5 *
4
4.5 *
5
6
8
10
12
14*
16
18*
20
22*
24
27*
30
33*
36
39*
42
45*
48
52*
56
60*
64
*
0.8
0.8
1
1.3
1.3
1.5
1.7
2
2.2
2.5
3
4
5
6
8
8
10
10
10
12
12
15
15
18
18
21
21
24
24
28
28
32
External threads
Fundamental
deviation
Tolerance
e
f
g
—
—
—
—
—
0.050
0.053
0.056
0.056
0.060
0.060
0.063
0.067
0.071
0.071
0.071
0.080
0.080
0.080
0.085
0.085
0.090
0.090
0.095
0.095
0.100
0.100
0.106
0.106
0.112
0.112
0.118
0.034
0.034
0.034
0.035
0.035
0.036
0.036
0.038
0.038
0.038
0.040
0.042
0.045
0.048
0.052
0.052
0.058
0.058
0.058
0.063
0.063
0.070
0.070
0.075
0.075
0.080
0.080
0.085
0.085
0.090
0.090
0.095
0.019
0.019
0.019
0.020
0.020
0.020
0.021
0.022
0.022
0.024
0.026
0.028
0.032
0.034
0.038
0.038
0.042
0.042
0.042
0.048
0.048
0.053
0.053
0.060
0.060
0.063
0.063
0.071
0.071
0.075
0.075
0.080
Grade 6
Major Pitch
dia.
dia.
0.063
0.085
0.063
0.085
0.095
0.067
0.071
0.100
0.100
0.071
0.075
0.106
0.125
0.085
0.090
0.140
0.140
0.090
0.150
0.095
0.112
0.180
0.212
0.118
0.132
0.236
0.265
0.150
0.160
0.280
0.280
0.160
0.170
0.335
0.170
0.335
0.335
0.170
0.375
0.200
0.375
0.200
0.212
0.425
0.212
0.425
0.475
0.224
0.224
0.475
0.500
0.236
0.500
0.236
0.530
0.250
0.250
0.530
0.265
0.560
0.560
0.265
0.600
0.280
Second choice diameter.
COPYRIGHT
Grade 8
Major Pitch
dia.
dia.
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0.150
0.236
0.280
0.180
0.190
0.335
0.375
0.212
0.236
0.425
0.450
0.250
0.250
0.450
0.265
0.530
0.530
0.265
0.265
0.530
0.600
0.315
0.315
0.600
0.670
0.335
0.335
0.670
0.355
0.750
0.750
0.355
0.800
0.375
0.800
0.375
0.400
0.850
0.400
0.850
0.425
0.900
0.425
0.900
0.950
0.450
mil li metres
Internal threads
Fundamental
Tolerance
deviation
H
G
Grade 6
+
Minor Pitch
dia.
dia.
0.085
0.100
0.019
0
0.085
0.100
0.019
0
0.090
0.112
0
0.019
0.020
0.125
0.095
0
0.095
0.125
0
0.020
0.140
0.100
0.020
0
0.112
0
0.021
0.160
0.180
0.118
0.022
0
0.118
0
0.022
0.190
0.125
0.200
0
0.024
0.026
0.236
0.150
0
0.160
0.265
0
0.028
0.032
0.300
0.180
0
0.200
0
0.034
0.335
0.375
0.212
0.038
0
0.212
0
0.038
0.375
0.224
0.042
0.450
0
0.042
0.450
0.224
0
0.224
0.450
0
0.042
0.500
0.265
0
0.048
0.265
0
0.048
0.500
0.560
0.280
0.053
0
0.280
0.053
0.560
0
0.300
0.600
0
0.060
0.060
0.600
0.300
0
0.670
0.315
0
0.063
0.670
0.315
0
0.063
0.335
0
0.071
0.710
0.335
0.071
0.710
0
0.355
0.075
0.750
0
0.355
0.750
0
0.075
0.800
0.375
0
0.080
AS 1275—1985
12
TABLE 3.3
LIMITING DIMENSIONS FOR METRIC COARSE PITCH SERIES
SCREW THREADS
mill imetres
Basic
major
dia.
D, d
Pitch
P
Tolerance
class
1.6
0.35
1.8
0.35
2
0.4
2.2 *
0.45
2.5
0.45
3
0.5
3.5 *
0.6
4
0.7
4.5 *
0.75
5
0.8
6
1
8
1.25
10
1.5
12
1.75
6g
6f
6g
6f
6g
6f
6g
6f
6g
6f
6g
6f
6e
6g
6f
6e
6g
6f
6e
6g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
14 *
2
16
2
18
2.5
20
2.5
22 *
2.5
External threads
Major
Pitch
diameter
diameter
max.
min.
max.
min.
1.581
1.566
1.781
1.766
1.981
1.966
2.180
2.165
2.480
2.465
2.980
2.964
2.950
3.479
3.464
3.447
3.978
3.962
3.944
4.478
4.462
4.444
4.976
4.976
4.962
4.940
5.974
5.974
5.960
5.940
7.972
7.972
7.958
7.937
9.968
9.968
9.955
9.933
11.966
11.966
11.952
11.929
13.962
13.962
13.948
13.929
15.962
15.962
15.948
15.929
17.958
17.958
17.942
17.920
19.958
19.958
19.942
19.920
21.958
21.958
21.942
21.920
1.496
1.481
1.696
1.681
1.886
1.871
2.080
2.065
2.380
2.365
2.874
2.858
2.844
3.354
3.339
3.322
3.838
3.882
3.804
4.338
4.322
4.304
4.826
4.740
4.812
4.790
5.794
5.694
5.780
5.760
7.760
7.637
7.746
7.725
9.732
9.593
9.719
9.697
11.701
11.541
11.687
11.664
13.682
13.512
13.668
13.649
15.682
15.512
15.668
15.649
17.623
17.428
17.607
17.585
19.623
19.428
19.607
19.585
21.623
21.428
21.607
21.585
1.354
1.339
1.554
1.539
1.721
1.706
1.888
1.873
2.188
2.173
2.655
2.639
2.625
3.089
3.074
3.057
3.523
3.507
3.489
3.991
3.975
3.957
4.456
4.456
4.442
4.420
5.324
5.324
5.310
5.290
7.160
7.160
7.146
7.125
8.994
8.994
8.981
8.959
10.829
10.829
10.815
10.792
12.663
12.663
12.649
12.630
14.663
14.663
14.649
14.630
16.334
16.334
16.318
16.296
18.334
18.334
18.318
18.296
20.334
20.334
20.318
20.296
1.291
1.276
1.491
1.476
1.654
1.639
1.817
1.802
2.117
2.102
2.580
2.564
2.550
3.004
2.989
2.972
3.433
3.417
3.399
3.901
3.885
3.867
4.361
4.306
4.347
4.325
5.212
5.144
5.198
5.178
7.042
6.970
7.028
7.007
8.862
8.782
8.849
8.828
10.679
10.593
10.665
10.642
12.503
12.413
12.489
12.470
14.503
14.413
14.489
14.470
16.164
16.069
16.148
16.126
18.164
18.069
18.148
18.126
20.164
20.069
20.148
20.126
Minor
Stress
diameter area As
min.
mm 2
1.075
1.060
1.275
1.260
1.408
1.393
1.539
1.524
1.839
1.824
2.272
2.256
2.242
2.635
2.620
2.603
3.002
2.986
2.968
3.439
3.423
3.405
3.868
3.814
3.854
3.834
4.597
4.528
4.583
4.563
6.272
6.200
6.258
6.237
7.938
7.858
7.925
7.903
9.602
9.516
9.588
9.565
11.271
11.181
11.257
11.238
13.271
13.181
13.257
13.238
14.624
14.529
14.608
14.586
16.624
16.529
16.608
16.586
18.624
18.529
18.608
18.586
*
Second choice diameter.
1.27
Internal threads
TolerMajor
Pitch
ance diameter
diameter
class
min.
max. min.
Minor
diameter
max.
min.
5.03
6H
6G
6H
6G
6H
6G
6H
6G
6H
6G
6H
6G
1.600
1.600
1.800
1.800
2.000
2.000
2.200
2.200
2.500
2.500
3.000
3.000
1.458
1.477
1.658
1.677
1.830
1.849
2.003
2.023
2.303
2.323
2.775
2.795
1.373
1.392
1.573
1.592
1.740
1.759
1.908
1.928
2.208
2.228
2.675
2.695
1.321
1.340
1.521
1.540
1.679
1.698
1.838
1.858
2.138
2.158
2.599
2.619
1.221
1.240
1.421
1.440
1.567
1.586
1.713
1.733
2.013
2.033
2.459
2.479
6.78
6H
6G
3.500
3.500
3.222
3.243
3.110
3.131
3.010
3.031
2.850
2.871
8.78
6H
6G
4.000
4.000
3.663
3.685
3.545
2.576
3.422
3.444
3.242
3.264
6H
6G
4.500
4.500
4.131
4.153
4.013
4.035
3.078
3.900
3.688
3.710
14.2
6H
6G
5.000
5.000
4.605
4.629
4.480
4.504
4.334
4.358
4.134
4.158
20.1
6H
6G
6.000
6.000
5.500
5.526
5.350
5.376
5.153
5.179
4.917
4.943
36.6
6H
6G
8.000
8.000
7.348
7.376
7.188
7.216
6.912
6.940
6.647
6.675
58.0
6H
6G
10.000
10.000
9.206
9.238
9.026
9.058
8.676
8.708
8.376
8.408
84.3
6H
6G
12.000 11.063 10.863
12.000 11.097 10.897
10.441 10.106
10.475 10.140
115
6H
6G
14.000 12.913 12.701
14.000 12.951 12.739
12.210 11.835
12.248 11.873
157
6H
6G
16.000 14.913 14.701
16.000 14.951 14.739
14.210 13.835
14.248 13.873
192
6H
6G
18.000 16.656 16.376
18.000 16.642 16.418
15.854 15.294
15.786 15.336
245
6H
6G
20.000 18.600 18.376
20.000 18.642 18.418
17.744 17.294
17.786 17.336
303
6H
6G
22.000 20.600 20.376
22.000 20.642 20.418
19.744 19.294
19.786 19.336
1.7
2.07
2.48
3.39
11.3
(conti nued)
COPYRIGHT
13
AS 1275—1985
TABLE 3.3 (continued)
mill imetres
Basic
major
dia.
D, d
24
3
27 *
3
30
3.5
33 *
3.5
36
4
39 *
4
42
4.5
45 *
4.5
48
5
52 *
5
56
5.5
60 *
5.5
64
*
Pitch
P
6
Tolerance
class
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
6g
8g
6f
6e
External threads
Internal threads
Major
Pitch
Major
Pitch
Minor Stress Tolerdiameter
diameter
diameter
diameter area As ance diameter
class
max.
min.
max.
min.
min.
mm 2
min.
max.
min.
19.955
23.952 23.577 22.003 21.803
353
6H
24.000 22.316 22.051
19.840
23.952 23.352 22.003 21.688
6G
24.000 22.364 22.099
19.940
23.937 23.562 21.988 21.788
19.918
23.915 23.540 21.966 21.766
26.952 26.577 25.003 24.803
22.955
26.952 26.352 25.003 24.688
22.840
459
6H
27.000 25.316 25.051
26.937 26.562 24.988 24.788
22.940
6G
27.000 25.364 25.099
26.915 26.540 24.966 24.766
22.918
29.947 29.522 27.674 27.462
25.305
29.947 29.277 27.674 27.339
25.182
561
6H
30.000 28.007 27.727
29.930 29.505 27.657 27.445
25.288
6G
30.000 28.060 27.780
29.910 29.485 27.637 27.425
25.268
28.305
32.947 32.522 30.674 30.462
694
6H
33.000 31.007 30.727
28.182
32.947 32.277 30.674 30.339
6G
33.000 31.060 30.780
28.288
32.930 32.505 30.657 30.445
28.268
32.910 32.485 30.637 30.425
30.654
35.940 35.465 33.342 33.118
817
6H
36.000 33.702 32.402
30.523
35.940 35.190 33.342 32.987
6G
36.000 33.762 33.462
30.639
35.925 35.450 33.327 33.103
30.619
35.905 35.430 33.307 33.083
38.940 38.455 36.342 36.118
33.654
38.940 38.190 36.342 35.987
33.523
976
6H
39.000 36.702 35.402
38.825 38.450 36.327 36.103
33.639
6G
39.000 36.762 36.462
38.905 38.430 36.307 36.083
33.619
41.937 41.437 39.014 38.778
36.006
41.937 41 137 39.014 38.639
35.876 1121
6H
42.000 39.392 39.077
41.920 41.420 38.997 38.761
35.989
6G
42.000 39.455 39.140
41.900 41.400 38.977 38.741
35.969
44.937 44.437 42.014 41.778
39.066
44 937 44.137 42.014 41.639
38.867 1306
6H
45.000 42.392 42.077
44.920 44.420 41.997 41.761
38.989
6G
45.000 42.455 42.140
44.900 44.400 41.977 41.741
38.969
47.929 47.399 44.681 44.431
41.351
47.929 47.079 44.681 44.281
41.201 1473
6H
48.000 45.087 44.752
47.915 47.385 44.667 44.417
41.337
6G
48.000 45.158 44.823
47.894 47.364 44.646 44.396
41.316
51.929 51.399 48.681 48.431
45.351
51.929 51.079 46.681 48.281
45.201 1758
6H
52.000 49.087 48.752
51.915 51.385 48.667 48.417
45.337
6G
52.000 49.158 48.823
51.894 51.364 48.646 48.396
45.316
55.925 55.365 52.353 52.088
48.700
55.925 55.025 52.353 51.928
48.540 2030
6H
56.000 52.783 52.428
55.910 55.350 52.338 52.073
48.685
6G
56.000 52.858 52.503
55.888 55.328 52.316 52.051
48.663
59.925 59.365 56.353 56.088
52.700
59.925 59.025 56.353 55.928
52.540 2362
6H
60.000 56.783 56.428
59.910 59.350 56.338 56.073
52.685
6G
60.000 56.858 56.503
59.888 59.328 56.316 56.051
52.663
63.920 63.320 60.023 59.743
56.047
63.920 62.970 60.023 59.573
55.877 2676
6H
64.000 60.478 60.103
63.905 63.305 60.008 59.728
56.032
6G
64.000 60.558 60.183
63.882 63.282 59.985 59.705
56.009
Second choice diameter.
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Minor
diameter
max.
min.
21.252
21.300
20.752
20.800
24.252
24.300
23.752
23.800
26.771
26.824
26.211
26.264
29.771
29.824
29.211
29.264
32.270
32.330
31.670
31.730
35.270
35.330
34.670
34.730
37.799
37.862
37.129
37.192
40.799
40.862
40.129
40.192
43.297
43.368
42.587
42.658
47.297
47.368
46.587
46.658
50.796
50.871
50.046
50.121
54.796
54.871
54.046
54.121
58.305
58.385
57.505
57.585
AS 1275—1985
14
3.6.2
Disposition of tolerance classes.
The
tolerance classes are disposed about the basic pitch
and major diameter for external threads and the basic
pitch and minor diameter for internal threads as
shown in Fig. 3.2.
3.6.3 Selection of tolerance classes.
3.6.3.1 General. The tolerance classes for the pitch
and crest diameter, shall be selected in accordance
with Clause 3.6.3.3, bearing in mind the type of
fastener, i.e. ‘precision’ or ’commercial’ quality.
3.6.3.2 Length of axial thread engagement. The
tolerance classes given in this standard are intended
for the ‘normal’ length of thread engagement as given
in Table 3.2. If the actual length of thread
engagement is unknown (as in the manufacturing of
standard bolts), the normal length of thread
engagement shall be assumed.
NOTE: For further informati on, see AS 1721.
3.6.3.3 Recommended combinations. Although there
is no direct guidance given by ISO for the
combination of thread classes, these may be inferred
by reference to the appropriate ISO standards for
threaded fasteners.
Based on the above, the following combinations are
recommended:
(a) Commercial quality fasteners—6H nut with 8g
bolt.
(b) Precision quality fasteners—6H nut with 6g bolt.
NOTE: Tolerance classes 6e, 6f and 6G, are essenti ally provided
for ‘preplated’ screw thread dimensions.
3.7 LIMITS OF SIZE. The limiting dimensions for
external threads, tolerance classes 6e, 6f, 6g and 8g;
and internal threads, tolerance classes 6H and 6G are
given in Table 3.3.
3.8 COATED THREADS. The limiting dimensions
given in Table 3.3 apply to the screw threads before
coating, unless otherwise specified. After coating the
actual thread profile shall not transgress the
maximum material limits, i.e. the basic dimensions as
given in Table 3.1.
The above provisions apply to all coated screw
threads except those hot-dip galvanized in accordance
with AS 1214.
NOTE: For further informati on on electr oplated coati ngs on
threaded components, see AS 1897.
Fig. 3.2. RELATIVE POS ITION OF TOLERA NC E CLASS ES
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15
AS 1275—1985
SECTION 4. DESIGNATION OF SCREW THREADS
4.1 SCOPE OF SECTION. This Section sets out
the designation system used for metric screw threads
for fasteners, and gives the complete designation,
together with a shortened designation which may be
applied to coarse pitch series threads as covered by
this standard. Provision is also made for designating
different types of fits between internal and external
threads.
4.3 COMPLETE DESIGNATION FOR EXTERNAL
THREADS. The complete designation for an external
screw thread with the same tolerance class for the pitch
diameter and major diameter comprises the same
elements in the same order as given for internal screw
threads (see Clause 4.2).
4.2
COMPLETE DESIGNATION FOR
INTERNAL THREADS. The complete designation
of an internal screw thread to this standard comprises
the following elements in the following order:
Thread designation symbol
(a) The letter M indicating an ISO Metric general
purpose screw thread.
Pitch diameter tolerance class
(b) The value of the basic major diameter in
millimetres.
4.4 SHORTENED DESIGNATION FOR COARSE
PITCH SERIES THREADS. The designation for
coarse pitch series internal and external threads is the
same as that given in Clauses 4.2 and 4.3 respectively,
except that the indication of pitch may be omitted.
Therefore if no pitch is indicated in the designation, a
coarse pitch series thread is specified, i.e.—
M8 — 6e is the same as M8 × 1.25 - 6e; and
M5 — 5H is the same as M5 × 0.8 - 5H.
4.5 DESIGNATION OF A THREAD FIT. A fit
between mating internal and external threads is indicated
in the designation by the tolerance class of the internal
thread, followed by the tolerance class for the external
thread separated by an oblique stroke.
Example:
M8 - 6H/6g
(c) The value of the pitch in millimetres.
(d) The tolerance class designation for the pitch
diameter.
EXAMPLE:
Thread designati on symbol
Basic major diameter
Pitch
Pitch diameter tolerance class
M5 × 0.8 - 5H
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NOTE: For coarse pitch seri es threads, see also Clause 4.4.
EXAMPLE:
Basic major diameter
Pitch
M8 × 1 - 6g
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NOTE: For coarse pitch series threads, see also Clause 4.4.
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AS 1275—1985
16
APPENDIX A
NOTES ON THE PRODUCTION OF EXTERNAL THREADS
The actual form of the crest of an external thread depends on the method of
manufacture.
If a single-ribbed grinding wheel or single-point cutting tool is used, a thread with a
completely flat crest will be produced, as illustrated in Fig. A1(a).
Use of a crushed multi-ribbed wheel produces a crest profile similar to that shown in
Fig. A1(b).
A typical form of crest produced by the thread rolling processes is shown in
Fig. A1(c). The crests of threads resulting from this process will normally fall wholly
above the minimum limiting profile shown in Figs 2.6 and 2.7.
Fig. A1(d) shows the form of crest produced by a thread cutting die of nominal root
radius, viz 125P. With a correctly formed tool, there will be no serious loss of straight
flank even when it cuts a thread on minimum diameter.
Provided that due care is taken in regard to the wear of tools, rounded crests should
rarely reach the dotted profile shown in Fig. 2.3.
It may be mentioned that the following advantages are associated with bolts with
rounded crests:
(a) Bolts with rounded crests are less susceptible to damage by burring in handling
and transport than those having flat crests, which result in sharp, or semi-sharp,
edges round the outside diameter of the bolt.
(b) Troubles associated with plating are far less serious if the crests of the bolts are
rounded. In the plating of bolts by the usual barrel plating process, the burring of
flat-crested bolts can be quite serious, and in the still-vat process the plating tends
to build up round the two edges at the outside diameter and encroaches upon the
flanks.
(a) Crest produced by grinding wit h
a single-ri bbed wheel or cutt ing
with a single point tool.
(b) Crest produced by grinding wit h
a crushed mult i- ri bbed wheel.
(c) Crest produced by thread-r olling
(d) Crest produced by a thread
cutt ing die.
Fig. A1. CR ES T PR OFILES RES ULTING FROM DIFFER EN T PR ODUC TION METHODS
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17
AS 1275—1985
APPENDIX B
COMPARISON OF SYMBOLS (Notations) FOR SCREW THREAD PARAMETERS
Symbol (notation)
used in
ISO and
AS 1275—1972
this
standard
D
D; d
Dn
—
Ds
—
d 2; d 2
E
En
—
Es
d
D 1; d 1
—
dn
ds
d3 *
p
P
H
H
h
—
hn
—
hs
—
—
—
h”n
h′s
Parameter
Major diameter — basic
internal threads
external threads
Pitch diameter — basic
internal threads
external threads
Minor diameter — basic
internal threads
external threads
Pitch
Height of fundamental tr iangle
Height (depth) of thread — basic
internal threads
external threads
Addendum — basic
internal threads
external threads
Dedendum — basic
internal threads
external threads
Truncati on at minor diameter — basic
internal threads
external threads
Truncati on at major diameter — basic
internal threads
external threads
Width of fl at at minor diameter — basic
internal threads
external threads
Width of fl at at major diameter — basic
internal threads
external threads
Radius at minor diameter— external threads
Radius at major diameter— internal threads
Height of circular segments at rounded roots — internal threads
external threads
Tolerances for pitch diameter — internal threads
external threads
Tolerances for major diameter — internal threads
external threads
Tolerances for minor diameter — internal threads
external threads
Areas of str ess calculation
Tension
Shear
Deviations—general
symbols
Fundamental deviati on series
External threads cross-secti on — stress areas
core area
External thread heli x
Internal thread helix
Internal threads — lower
upper
External threads — lower
upper
Internal threads (L n)
External threads (U s)
Radial engagement
NOTE: The following addit ional symbols are used in the ISO standards but not in this standard:
EI = lower deviation for internal threads
ES = upper deviation for internal threads
ei = lower deviation for external threads
es = upper deviati on for external threads
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h′ n
h”s
t
tn
ts
T
Tn
Ts
—
—
—
—
—
f
fn
fs
—
—
—
F
Fn
Fs
rs
Rn
—
—
—
R
—
Cn
Cs
—
—
T En
T Es
T D2
T d2
T Dn
T Ds
—
Td
T dn
T ds
T1D
As
Ac
AS s
AS n
ln
un
ls
us
H, G
h, g, e
Re
—
As
—
—
H; G;
h; g; e; f
—
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