Tapered thread – chart, sizes, designations

The main image of article about tapered threads

What is a tapered thread?

A tapered thread is a type of thread that has a cone shape. If you look at it in profile, you will notice that it tapers to one side - unlike traditional threads, which remain straight throughout.

This thread design means that the tapered threads provide very high connection tightness even without the use of additional seals.

What is the difference between tapered threads and cylindrical threads?

The main difference between a tapered thread and a cylindrical thread is in their construction. A cylindrical thread is formed on the cylindrical surface, meaning that it retains a uniform diameter throughout its length. Whereas, a tapered thread is formed on the surface of a cone, meaning that it is gradually tapered.

Comparison of a tapered thread and a cylindrical thread

There are two further important differences between the above.

Firstly, the tapered thread is primarily found as an inch tapered thread (less frequently as a metric tapered thread). Secondly, because of its sealing properties, the tapered thread variant is used in slightly different situations, as you will read later in this article.

What are the designations of the tapered thread?

Tapered thread is designated by the manufacturer presenting particular types of thread. Here are a couple of examples of the tapered thread designations:

  • St. M - metric thread, tapered; 
  • R (also BSPT) - pipe thread, tapered, male; 
  • Rc - pipe thread, tapered, internal; 
  • St. B (also NPT) - Briggs tapered pipe thread; 
  • W - tapered thread for gas valves.

As you can see, the tapered shape does not have its own individual designation. Furthermore, it is worth adding that most threads (R, Rc, NPT, W) are of Anglo-Saxon origin, so manufacturers give their dimensions in inches.

What is the application of tapered threads?

Tapered threads are most often used as a connection for:

  • water pipes, 
  • fuel pipes, 
  • lubricant pipes, 
  • gas pipes.

Interestingly, the large-angle tapered thread was once often used in cameras, or more precisely: in their release cables. Tapered threads provide a tight connection without the necessity of additional sealing.

What are the dimensions of the tapered thread?

As the tapered thread is found in many variations, it is difficult to provide all possible product dimensions. Therefore, in the chart below, we have focused only on their most popular variations.

Calliper measurement Calliper measurement Gauge measurement Gauge measurement Thread type Thread type
Outer diameter [mm] Inner diameter [mm] Number of coils per inch Thread pitch [mm] Inch pipe BSP BSPT Inch pipe NPT NPTF
9.3 ÷ 9.7 8.5 ÷ 8.9 28 (0.91) 1/8”  
9.3 ÷ 9.7 8.5 ÷ 8.9 27 (0.95)   1/8”
12.9 ÷ 13.1 11.4 ÷ 11.9 19 (1.34) 1/4”  
12.9 ÷ 13.1 11.4 ÷ 11.9 18 (1.41)   1/4”
16.3 ÷ 16.6 14.9 ÷ 15.4 19 (1.34) 3/8”  
16.3 ÷ 16.6 14.9 ÷ 15.4 18 (1.41)   3/8”
20.5 ÷ 20.9 18.6 ÷ 19.0 14 (1.81) 1/2”  
20.7 ÷ 21.1 18.3 ÷ 18.7 14 (1.81)   1/2”
22.6 ÷ 22.9 20.6 ÷ 21.0 14 (1.81) 5/8”  
26.1 ÷ 26.4 24.1 ÷ 24.5 14 (1.81) 3/4”  
26.3 ÷ 26.7 23.7 ÷ 24.1 14 (1.81)   3/4”
29.8 ÷ 30.2 27.8 ÷ 28.1 14 (1.81) 7/8”  
33.0 ÷ 33.2 30.3 ÷ 30.8 11 (2.31) 1”  
32.9 ÷ 33.4 30.3 ÷ 30.8 11.5 (2.21)   1”
37.6 ÷ 37.9 34.8 ÷ 35.1 11 (2.31) 1.1/8”  
41.5 ÷ 41.9 39.0 ÷ 39.5 11 (2.31) 1.1/4”  
41.4 ÷ 42.0 39.2 ÷ 39.6 11.5 (2.21)   1.1/4”
47.4 ÷ 47.8 44.8 ÷ 45.3 11 (2.31) 1.1/2”  
47.3 ÷ 47.9 45.1 ÷ 45.5 11.5 (2.21)   1.1/2”
59.4 ÷ 59.8 56.5 ÷ 56.8 11 (2.31) 2”  
59.9 ÷ 60.2 56.4 ÷ 56.7 11.5 (2.21)   2”
65.4 ÷ 65.7 62.7 ÷ 63.0 11 (2.31) 2.1/4”  
72.7 ÷ 73.0 68.8 ÷ 69.1 8 (3.175)   2.1/2”
74.9 ÷ 75.2 72.2 ÷ 72.5 11 (2.31) 2.1/2”  
87.5 ÷ 87.9 84.9 ÷ 85.3 11 (2.31) 3”  
88.5 ÷ 88.9 84.7 ÷ 85.1 8 (3.175)   3”
112.6 ÷ 113.0 110.1 ÷ 110.5 11 (2.31) 4”  
113.9 ÷ 114.3 110.2 ÷ 110.6 8 (3.175)   4”
138.0 ÷ 138.4 135.5 ÷ 135.9 11 (2.31) 5”  
139.8 ÷ 141.3   8 (3.175)   5”
163.4 ÷ 163.8 160.9 ÷ 161.4 11 (2.31) 6”  
167.8 ÷ 168.3   8 (3.175)   6”
218.5 ÷ 219.0   8 (3.175)   8”
Photo of Bartosz Kułakowski - CEO of Hosetech sp. z o. o.

Articles author

Bartosz Kułakowski

CEO of Hosetech Sp. z o.o.

Bartosz Kulakowski is an industrial hoses and couplings specialist with over 10 years of experience. Bartosz has been present in the technical industry since 2013. He gained experience as a technical and commercial advisor in the sector of plastic conveyor belts, steel structures, industrial hoses, and connectors. Since 2016, he has specialized exclusively in hoses and connectors. In 2019 he opened his own business under the HOSETECH Bartosz Kulakowski brand and since July 2022 he has been the CEO of the capital company HOSETECH Sp z o. o. (LLC).

SPIS TREŚCI

What is a tapered thread?

What is the difference between tapered threads and cylindrical threads?

What are the designations of the tapered thread?

What is the application of tapered threads?

What are the dimensions of the tapered thread?

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