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4.3.2 PIPE CYLINDER SCREW-THREAD

A pipe cylinder screw-thread is a fastener and it is mainly used for connection of water- and
gas pipelines and armature. The thread profile is shown in fig. 4.4.
Conventional denotations of a pipe cylinder screw-thread consist of (fig.4.5): Latin letter G; a
nominal conventional size in inches; an accuracy class of middle diameter and general denotation
for a left-hand thread in case of need.

Figure 4.4 - Pipe cylinder thread profile

Figure 4.5 - The conventional drawing of a pipe cylinder thread:
a) on a pipe; b) in an opening.

There are two accuracy classes A and B. An examples of a pipe cylinder screw-thread
conventional denotation with a nominal size of 1 inch are: G1–A (for the accuracy class A); G1LH
– B (for the left-hand thread of the accuracy class B).
It is necessary to remember, that the size of a pipe cylinder thread is not measured on an
external diameter – d. Unlike metric and other threads the nominal size of a pipe cylinder thread is
marked in inches, here it approximately equals the internal diameter of a pipe, where a screw-thread
is cut on. A pipe cylinder thread of the same size can be cut on as on pipes with the different pipe
wall thickness as well as on a continuous bolt. Parameters of a pipe cylinder thread according to
State Standard 6357-81 are shown in table 4.2.

Table 4.2 - Sizes of a pipe cylinder thread for diameters from 1/4” to 2”(first row)

Conditional pass Thread diameter, mm Thread pitch
diameter of a pipe Dy P, mm
in inches in mm External -d Internal –d 1
1/4 8 13.158 11.446 1.337
3/8 10 16.663 14.951 1.337
1/2 15 20.956 18.532 1.814
3/4 20 26.442 24.119 1.814
1 25 33.250 30.292 2.309
1 1/4 32 41.912 38.954 2.309
1 1/2 40 47.805 44.847 2.309
1 3/4 45 53.750 50.791 2.309
2 50 59.616 56.659 2.309

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