Understanding the Different Types of Fastener Threads

Custom threaded fasteners are critical components in a variety of industrial and commercial equipment. They are known for a variety of benefits, which include their strength, ease of installation, cost-effectiveness and removability.  They are also available in different sizes for a myriad of applications.

Despite all these benefits, purchasing different types of threaded fasteners is not an easy task. The simple reason for this is there are too many models of one fastener out there. You can eliminate many models by considering a few aspects like material, size, and thread type. While many customers are familiar with sizes and materials, they may not be aware of different types of threads. We decided to address this issue by providing this post.

Understanding Basic Thread Designs

Generally, fastener threads are designed in two ways – as coarse or fine threads. Each design has its own benefits. Let’s take a look at them.

  • Coarse Threads: These threads are designed with large thread heads and higher flank engagement. Coarse threads provide resistance from nicking or any other kind of damage. They are easy to install and do no suffer from galling and assembly issues. For these reasons, fasteners with coarse threads are generally chosen for industrial applications.
  • Fine Threads: Fine threads are designed to have stronger shear and tension capabilities. This is because the threads are manufactured with small diameters and large tensile stress areas. Fine threads allow for greater fastener adjustment in an application. They can be used in thin wall sections as well as materials that may be difficult to tap.

Types of Fastener Threads

The following points will help understand the different thread types that are used to manufacture custom threaded fasteners:

  • Unified National Coarse (UNC): This is the most common thread type used in most fasteners. UNC threads do not require cross threading during manufacturing and are known for their high tolerance levels. The reasons are they help the fastener fit deeper in the application but can also be removed easily.
  • Unified National Fine (UNF): This thread type is popular for fasteners used in industries like aerospace. They are designed with extremely tight tolerances and tension adjustments. UNF threads are also known for carrying heavy loads. Hence, they are used in applications that require exact fastener fitting.
  • United National Extra Fine (UNEF): A thread type designed to be finer than UNF threads, UNEF threads are unique as they are used in specialized applications. These can include thin threaded walls and tapped holes in hard and thin materials.
  • UNJC and UNJF Threads: These “J” thread types are mainly used when manufacturing bolts. The threads can be made either on the interior or the exterior of a fastener. For bolts, manufacturers prefer creating exterior threads, as they create a small area of stress, a large root radius and tensile area.
  • UNK and UNR Threads: Both UNK and UNR are external threads. UNR threads are similar to UNC threads, but with a greater rounded radius. UNK threads are similar to UNR threads, however, they have minor root radii and diameter.

If you still require more information about these thread types the best option is to contact us a well-known fastener manufacturer. Norwood Screw Machine Parts provides a variety of custom threaded fasteners for different applications.

About Norwood Screw Machine

Norwood is a privately owned custom screw machine parts manufacturer. For over 59 years we serve some of the largest corporations to the small company with a new product to develop. Whether a unique item with a one time requirement or a long running contract order with scheduled deliveries, Norwood Screw Machine Parts is the right choice for the job.


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