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UDC 62'l.#2.0)2.22
IS0
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION
IS0 RECOMMENDATION
R7
PIPE THREADS
FOR GAS LIST TUBES AND SCREWED FITTINGS
WHERE PRESSURE-TIGHT JOINTS ARE MADE ON THE THREADS
(1/8 inch to 6 inches)
1'' EDITION
May 1955
COPYRIGHT RESERVED
The copyright of IS0 Recommendations and IS0 Standards
IS0 Member Bodies. Reproduction of these
belongs to
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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FOREWORD
This IS0 Recommendation No 7 was prepared by Technical Committee
ISO/TC 5-Pipes and Fittings-the Secretariat of which is held by the Asso-
ciation Suisse de Normalisation.
At its first meeting held in Zurich from 28 to 30 May, 1951, this Technical
Committee resolved to take the dimensions of the British Standard B.S. 21:
1938 as the basis for threads for gas list tubes and fittings. This decision con-
firmed the resolution adopted in 1938 by Technical Committee ISA 5 b-
Fittings-of the former International Federation of the National Standardizing
Associations (ISA).
The study of a proposal was entrusted to Sub-Committee ISO/TC 5/SC 5
-Fittings-the Secretariat of which is also held by the Association Suisse
de Normalisation. This Sub-Committee met for the first time on 26 October
1951 and adopted the following resolution :
“For the screw threads of gas list tubes and screwed
fittings, Sub-Committee ISO/TC 5/SC 5 proposes
to adopt a table made up as follows:
1. The drawings of the threads in the Standard B.S.
21: 1938, pages 5 and 6.
2. Column headings corresponding to those of
columns 1 and 6 to 11 of table 1, page 8, and of
columns 2 to 10 of table 3, page 10, of the Stand-
ard B.S. 21: 1938.
3. Numerical values (up to and including 6 inches
only) converted into millimetres on the basis of
1 inch = 25.4 mm), these values to be rounded
to the nearest thousandth of a millimetre, in the
case of the diameters of the threads and to the
nearest tenth of a millimetre for the linear
dimensions.”
ln December 1951, a Draft Proposal based on the foregoing data was
distributed to the Members of the Technical Committee. At its second plenary
meeting held in Milan from 7 to 10 April 1952, the Technical Committee decided
to adopt this Draft Proposal, with a few amendments, as a Draft IS0 Recom-
mendation.
This Draft IS0 Recommendation (No 14) was submitted to all the IS0
Member Bodies on 1 September, 1952, and was approved by the majority.
Taking into consideration the observations made by various Member Bodies,
Sub-Committee ISO/TC 5/SC 5 (at its Pans meeting of 17 and 18 September
1953) revised the text of the Draft, making certain modifications thereto.
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This revised text, which corresponds to that of the present Recommen-
dation, has been approved by the following 25 Member Bodies:
Australia Hungary New Zealand
Austria India Norway
Belgium Ireland Pakistan
Chile Israel Portugal
Denmark Italy Spain
Finland Japan Sweden
France Mexico Switzerland
Germany Netherlands United Kingdom
Yugoslavia
The revised text of the Draft IS0 Recommendation was submitted by
correspondence to the Members of the IS0 Council who, in May 1954, decided
to accept it as an IS0 RECOMMENDATION.
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IS0 Recommendation R7 May 1954
PIPE THREADS
FOR GAS LIST TUBES AND SCREWED FITTINGS
WHERE PRESSURE-TIGHT JOINTS ARE MADE ON THE THREADS
(118 inch to 6 inches)
A. SCOPE
The dimensions of the pipe threads given in Tables 1 and 2 relate to screwed
tubes and to threads in cocks, valves and any fittings to be connected to screwed
tubes.
B. DIMENSIONS
The dimensions shown in Table 1 have been taken from British Standard
B.S.21: 1938 -“Pipe threads, Part I: Basic sizes and tolerances”.
These dimensions have been converted into millimetres on the basis of
1 inch = 25.400 mm, beginning with the basic values, i.e. the number of threads
per inch which determines the pitch p, the formula h = 0.640327 p (the depth
of thread), and the major diameter at the gauge plane (gauge diameter), and
are shown in Table 2.
The values in Table 2 for the pitch, the depth of thread and the major
diameter at gauge plane are computed in ten-thousandths of a millimetre and
rounded to the next thousandth of a millimetre. The effective diameter and
the minor diameter are obtained by subtraction of the depth of thread from the
major diameter at gauge plane:
Col. 6 = COI. 5 - COI. 4
Col. 7 = Col. 5 - 2 x Col. 4
The basic gauge length, the tolerances and the fitting allowance are com-
puted in hundredths of a millimetre and rounded to the next tenth of a mil-
limetre.
The lengths in columns 11, 12, 15, 16 and 17 are obtained by addition or
by subtraction of the basic gauge length and the tolerance of the gauge length
or the fitting allowance respectively:
Col. 11 = Col. 8 + Col. 9
Col. 12 = Col. 8 - Col. 9
COI. 15 = Col. 8 + Col. 18
Col. 16 = COI. 11 + COI. 18
COI. 17 = Col. 12 + Col. 18
Bearing in mind that the lengths in the British Standard B.S. 21: 1938
are based on simple fractions of turns, and that the gauging practice operates
with numbers of turns of thread, the limits of tolerance have been alternatively
expressed in terms of actual linear dimensions in millimetres and of number
of turns of thread.
Table 1 gives the dimensions in inches and Table 2 in millimetres.
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Pipe Threads for Gas List Tubes and !
where Pressure -Tight Joints are made
(118 inch to 6 inches)
I Fig. 1. Parallel Thread
Usetu1 threod Inot leu than gauge length plus fitting ollow
H = 0.960491 x p
h = 0.640327 x p
r = 0.137329 x p
I
I
Fig. 2 Taper Thread
H = 0
...