Tapered thread – chart, sizes, designations

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.

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.