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а) б)
Figure 4.9 - Conventional drawing of a trapezoidal thread:
a) on a pipe; b) in an opening.

Denotation of a thread (fig.4.9) consists of the the Latin letters T r , external (nominal)
diameter and other parameters in accordance with the general rules of marking the threads.
The example of the conventional denotation of threads is with the nominal diameter 36 mm:
1. Tr36x18(P6)LH-8H – triple thread with a thread lead 18mm and a pitch 6mm, internal,
with the tolerance band 8Н, left-hand;
2. Tr36x6-6g – a external thread with the tolerance band 6g and a pitch 6mm, right-hand.

4.3.5 BUTTRESS THREAD

A buttress thread is used as leading. It is used to transmit great power in one direction for
example in jacks, presses, etc. Profile of a buttress thread is shown in fig. 4.10 according to State
Standard 10177-82. The sizes of nominal diameters and pitches coincide with the proper parameters
of a trapezoidal thread.
Thread denotations consists of the Latin letter S, external (nominal) diameter and other
parameters according to the general rules of marking the threads.
Example of conventional denotation of a buttress screw-thread with the nominal diameter
80mm, the pitch 10mm, an external thread with the tolerance band 7h: S80x10-7h.

Figure 4.10 - A buttress thread profile

а) b)
Figure 4.11 - Conventional drawing of a buttress thread:
a) on the outside; b) in an opening.

4.3.6 SQUARE NON-STANDARD THREAD

The profile of a square non-standard thread (fig.4.12) is rectangular or square. The thread
doesn’t have a conventional denotation, that is why all sizes of the thread (fig. 4.13) are marked on
the drawing. It is used as a leading thread (for example, in jacks etc.)

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