Basics of Thread Technology: Everything You Need to Know

If you're new to thread technology or venturing off the beaten path into the jungle of thread standards, you may feel a bit overwhelmed by data and technical terms that are hard to assign. Our beginner-friendly overview will help you get your bearings.

Overview of Thread Types: These Variants Can Be Distinguished

Although the fastening screw is the most common example of thread use, threads can do much more. However, their geometry and dimensions must be tailored to the desired application. This includes values such as the flank angle and the outer diameter, as well as the shape of the thread profile.

Over time, many different types of threads have emerged. We’ll take a closer look at the most important groups here.

Fastening Threads vs. Motion Threads

Fastening threads, such as those found on screws and nuts, are usually used to connect two components. The focus here is on a firm hold. Motion threads are a different story.

The profile of motion threads is designed to allow easy movement. This is useful for lead screws, worms, and spindles – wherever a rotary movement needs to be converted into an axial one.

Common motion threads include:

• Round thread
• Trapezoidal thread
• Saw thread

The round thread is also known for its robust design and is used for fastening in harsh work environments or in very frequently moving threads.

Standard Threads or Coarse Threads vs. Fine Threads

Many commonly used fastening threads are available not only as standard threads but also in one or more fine thread variants. Fine threads are characterized by a particularly small pitch. This results in good self-locking and allows for very fine control of the distance a threaded part moves per rotation.

Fine threads are used wherever precise adjustment is needed. Also on components exposed to frequent vibrations – because this increases the risk of threaded connections loosening on their own.

On the other hand, fine threads are also particularly sensitive. A general rule is to use them only where their benefits can truly shine. In all other cases, more robust standard threads are the better choice.

Metric Threads vs. Imperial Threads

The different measurement systems worldwide have also influenced the development of threads. While the metric system has been established in Europe and many other countries, imperial units are still commonly used in the Anglo-American world.

The main difference lies in the pitch. In metric threads, this refers to the distance between two thread peaks. In imperial threads, a number indicates the number of threads per inch. This value is abbreviated as TPI – threads per inch.

Threads for Special Applications

In various fields, very specific types of threads with special characteristics have developed. For example, threads for pipes, conduits, and fittings in plumbing, heating, and air conditioning are commonly referred to as pipe threads.

Other thread types are even more specialized, such as valve threads, bicycle threads, or PG conduit threads used in electrical installations. Sometimes existing thread types are modified to meet specific requirements – such as in aerospace applications using the MJ aerospace thread, which is based on the metric ISO thread.

Thread Standards and Specifications: ISO Threads and More

Standards and specifications play a major role in the world of thread technology. They ensure that screws, spindles, and other components remain reproducible and interchangeable. Whether you’re shopping in Germany or Japan – an M3 screw will always have the same dimensions.

Common standards can be divided into three groups based on their origin and geographic spread: metric threads, and British or American imperial threads. In addition to national standards organizations such as the German Institute for Standardization (DIN), many standards are also listed by the International Organization for Standardization (ISO), resulting in combinations like DIN ISO.

Metric ISO Thread

The metric ISO thread is primarily used in Europe. The standard thread is defined in DIN 13-1 and is complemented by fine threads in DIN 13-2 to DIN 13–11. It has a flank angle of 60° and is designated by the letter M and the nominal diameter.

British Threads

British thread standards follow the specifications of the British Standards Institution (BSI). The coarse thread is known as British Standard Whitworth (BSW), named after the father of thread standards, Joseph Whitworth. It has a flank angle of 55°, and dimensions are given in inches. The term “Whitworth thread” is commonly used for other British threads as well, particularly for the imperial pipe thread common in Germany. In addition to BSW, the BSF fine thread and other British standards exist.

American Threads

In the American market, there is a wide variety of imperial thread standards based on the Unified Thread Standard (UTS). The coarse Unified National Coarse (UNC) thread is complemented by the fine threads UNF and UNEF. The flank angle for these threads is 60°.

American thread standards also include many types of pipe threads for various applications. The ACME trapezoidal thread is also well known and is used, for example, in aircraft manufacturing.

Thread Manufacturing: Available Methods

Various methods are used to manufacture threads. In general, a distinction is made between cutting and forming methods.

The classification is simple:

• In cutting methods, material is removed – chips are produced.
• In forming methods, material is displaced – no chips are produced.

Each group includes further subcategories. The best approach depends on numerous factors, such as machine availability, the material used, and the intended use of the manufactured threads.

Thread Cutting

Thread cutting or tapping is one of the cutting methods. It is suitable for all types of threads and can be used in hobbies, crafts, and industrial manufacturing across all sectors. This makes thread cutting especially versatile. Thanks to its low entry barrier, it’s also suitable for DIY applications.

Thread Milling

Thread milling also removes material. Unlike a tap, a milling tool can produce both internal and external threads and various diameters. This method uses modern technologies such as CNC machines and is mainly used in industrial and series production.

Thread Turning

Thread turning can be performed on any standard lathe, making it suitable for smaller workshops. This is also a cutting method, which is flexible but requires experience and a good feel for precision to achieve optimal results.

Thread Forming or Rolling (Internal)

Thread forming or flaring looks similar to tapping at first glance. However, in this process, no material is removed – it is merely displaced. This creates high-quality surfaces and avoids chip-related problems. However, this method is only suitable for specific materials. Due to high friction, heat develops, which requires special attention to cooling.

Thread Rolling (External)

Thread rolling also displaces material and is therefore chipless. This method uses special rolling dies that press the external thread profile into a bolt.

At BAER, you’ll find not only top-quality products for thread manufacturing but also first-class service. Contact our expert customer support team anytime with your questions and requests, and check out our unbeatable offers in the BAER online shop. We look forward to hearing from you!