A list of the 13 most important types of threads you should know
Today we would like to provide you with an overview of the most important types of threads that you should know. But first we would like to give you a short introduction to threads and explain important terms.
What exactly is a thread?
A thread is, simply explained, a profiled notch that runs in a wave-like and continuous manner around a cylindrical bolt.
As already described in our articles from the section History of Threads, threads are thousands of years old. Threads accompany us in our everyday life. Not always visible. We are not really aware of the benefits they have for us. But they are used everywhere. For example, in our motor vehicles, right up to when we put on our reading glasses. The connectors make our lives easier and literally hold everything together.
As versatile as they are in use, there are very special requirements and loads on the threaded parts. A fundamental distinction is made between:
- Mounting thread
- Transmission thread
- Transport thread
Fastening thread is probably the type of thread that most of you think of first. They are tight threads, as we find in nuts and bolts.
Movement threads, on the other hand, are thread types that convert rotary motion into linear motion.
Nowadays, we find transport threads in agricultural machines and in water conveyance in the form of screws.
Right-hand thread (RH) and left-hand thread (LH)
Usually clockwise threads (right-hand threads) are threads that can be fastened by turning them clockwise. Less common are left-handed threads (left-handed threads), which can be screwed together counterclockwise. This connection is always used if it is to be avoided that the thread could loosen due to the self-movement. As for example with the left-hand bicycle pedal. The left-hand thread can be recognized by the abbreviation LH, while the right-hand thread has the abbreviation RH.
Pipe threads are threads that are used in water and gas installations. The ends of the pipes can have internal and external threads. On the one hand, a distinction is made between tapered and conical pipe threads, which are self-sealing. On the other hand, there are cylindrical pipe threads which are not self-sealing and require sealing agents such as hemp. The most important pipe threads are dealt with in more detail in our list
Why the different thread types?
The different types of threads result from historical developments and cultural preferences. In addition, there are different thread standards due to special requirements on the load-bearing capacity. The thread form is a decisive factor here.
What are the 13 most important thread types?
Here we want to give you an overview of the 13 most important thread types. The thread types are sorted according to country-specific types. Our list is by no means to be understood chronologically according to importance. Among the most important threads are:
ISO thread types
For the metric ISO thread types, the dimensions are always given in millimetres. The pitch is calculated by measuring the distance between the first and second tooth.
1 . ISO metric thread (M)
The ISO metric thread is a worldwide standardized thread and is probably the best known and most used in Europe. It is also known as a standard thread. Pitch and diameter are measured in millimetres. The code letter for the metric thread is M. The flank angle is 60 degrees. Furthermore, this type of thread is precisely defined in DIN 13 and DIN 14. DIN is the German Institute for Standardization.
2 . ISO metric fine thread (MF)
The ISO Metric Fine Thread is similar to the bigger brother of the ISO Metric Thread. Here the code letters are MF and the flank angle is 60 degrees. However, both differ in the pitch. The metric fine thread is used for example for watches.
3 . Steel conduit thread (Pg)
The steel armoured pipe thread or armoured thread (Pg) is a historical thread that was used in electrical engineering and is defined in DIN 40430. It is increasingly being replaced by metric threads (DIN EN 50262). The flank angle of the armoured pipe thread is 80 degrees.
4 . Trapezoidal thread (Tr)
The trapezoidal thread owes its name to the profile of the threads, which have the shape of a symmetrical trapezoid. The trapezoidal thread bears the identification letters Tr and has a flank angle of 30 degrees. There are three different standards. DIN 103 defines the ISO metric trapezoidal thread. In DIN 380 the flatter trapezoidal thread. And finally in DIN 30295 the rounded trapezoidal thread. Further information can be found in this article: Trapezoidal thread spindle.Beitrag: Trapezgewindespindel.
American thread types
For the American thread types, the dimensions are always given in inches (1 inch = 25.4 mm). The flank angle is always 60 degrees. The main difference between the various American unified threads is the pitch of the threads. These are also indicated in threads per inch. To determine the pitch, the number of threads is counted in one inch.
5 . Unified National Coarse Thread (UNC)
The Unified screw thread is a standard thread, which is mainly used in the USA and is the American equivalent of the Metric ISO thread. Only the unit of measurement inch instead of centimeter is used. The flank angle is – as with the ISO thread – 60 degrees.
6 . Unified National Fine Thread (UNF)
The same applies to the Unified National Fine thread type, which is the American fine thread to the ISO metric fine thread. As with the UNC, the flank angle is 60 degrees.
7 . Unified National Special Thread (UNS)
The thread type UNS is a special thread, which differs from the other Unified-threads in the pitch. Here, too, the flank angle is 60 degrees. This thread type is used for microphone stands, among other things.
8 . National Taper Pipe (NPT)
The thread type National Taper Pipe (NPT) is a tapered or conical pipe thread which is used for pipe fittings. The flank angle here is 60 degrees. Unlike NPTF, it is only self-sealing at low pressure.
9 . National Taper Pipe Dryseal (NPTF)
The NPTF is a tapered or conical pipe thread, which is self-sealing and has a flank angle of 60 degrees. The main difference to the NPT thread is that the internal and external threads overlap and can therefore be self-sealing without the use of sealant.
British Whitworth threads
The Whitworth thread is named after its inventor Sir Josep Whitworth. The British engineer introduced the world’s first thread standardization in 1841 and thus influenced the mass production of threads. The Whitworth thread is specified in inches and has a flank angle of 55 degrees. This type of thread is mainly used in the British Kingdom.
10 . British Standard Whitworth Coarse (BSW/ WW)
The British Standard Whitworth is on the one hand a standard thread and on the other hand a screw thread. It is often abbreviated with the abbreviation W or WW. In terms of meaning and use, it is equivalent to the ISO metric thread. It is specified in inches and has a flank angle of 55 degrees.
11 . British Standard Fine (BSF)
The British Standard Fine is the English variant of the fine thread. The meaning and use corresponds to that of metric fine thread. The thread is also specified in inches for the BSF and has a 55 degree flank angle.
12 . British Standard Pipe (BSP/ G)
The British Standard Pipe is a Whitworth pipe thread. It is a cylindrical thread and therefore not self-sealing. It is abbreviated with the abbreviation G. A small special feature is that the inch specification does not correspond to the inch diameter. For example: BSP 1″ = approx. 33.25 mm.
13 . British Standard Pipe Taper (BSPT/ R)
Whereas the British Standard Pipe Taper has a tapered external thread and a cylindrical internal thread. It is often abbreviated as R (tapered male thread) and Rp (cylindrical female thread). It is self-sealing in itself.
These were the 13 most important types of threads that you should know about. Do you have any questions or suggestions? Is a thread type important to you missing? Please do not hesitate to contact us or leave us a comment.