Glossary: thread

Whether you are a private individual or a professional, dealing with incompatibility between screws, threads and nuts is quite common. There are many thread types with different dimensional standards, strengths and finishes. To choose the right match, you must accurately determine the diameter and the thread pitch. Before anything else, it is essential to define the key terms used to understand the different types of threads.

What is a thread?

A thread refers to the set of helical ridges that make up a screw (for all types of screws, including plastic screws) or a nut. In other words, a thread is the helix formed by the thread flank.

What is a thread ridge?

The thread ridge is the threaded part of the screw. It can be identified by its helical grooves made of crests and roots. Their shape may vary depending on the standard. You therefore need to ensure compatibility between the two threaded components to achieve a perfect fit.

You can distinguish a male thread from a female thread by looking at where the thread is located. To keep it simple: the male part is on the outside of the fitting, while the female part is inside it.

The thread angle

This is the angle between two thread flanks. Like the pitch, it can vary depending on the thread standard.

Different thread types and pitch

The thread pitch is the distance (in millimeters or inches depending on the standard) between two crests of the thread. More simply, it refers to the spacing between the ridges. The pitch value is the distance traveled in one full turn. Here are the main thread pitch standards:

• ISO metric thread

  This thread has two versions: coarse pitch (standard pitch) and fine pitch (closer ridges). This triangular thread is one of the most used worldwide. In general (with some variants), its thread angle is 60 degrees. Note that fine-pitch metric threads are used when you do not have enough depth to tighten properly. As a guideline, the symbol for a standard metric thread is M (example: "slotted round head screw M2") and MF for fine pitch.

• American threads: UNC (Unified National Coarse) and UNF (Unified National Fine)

  Like British threads, UNC threads are expressed in inches and have a 60 degree angle. UNF threads are basically the inch-based equivalent of fine metric threads, used when depth is limited and proper tightening is required. Overall, American threads are widely used in the automotive industry.

• British Whitworth threads: BSW (British Standard Whitworth) and BSF (British Standard Fine)

  The Whitworth thread (also known as a gas thread) was the first standardized thread. It is commonly used in piping and is expressed in inches. Its thread angle is 55 degrees. There are two versions: BSW and BSF (fine pitch). BSW is often used for heavy mechanics such as agricultural machinery. BSF is used for older machines and vehicles.

• Gas threads

  Gas fittings can have a cylindrical or tapered thread with a parallel (straight) thread form. The number of threads per inch is expressed in inches. It is very commonly used in plumbing, piping, hydraulics and pneumatics.

Would you like more information about the thread types offered by Ajile?

All information regarding plastic nuts and plastic screws (with thread standards indicated) offered by Ajile can be found in the product pages.

Ajile, an expert in plastic hardware, offers high-quality products for professionals, public authorities and private customers.

Also discover a wide range of plastic bolts and threaded rods for all your projects, available to buy online on our website.

Browse our plastic screw range or contact an Ajile specialist to find out which thread type to choose if you are unsure. For reliable plastic components: plastic operating nuts, plastic screws, screw covers and many other products, choose Ajile!

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