If you are just beginning on the wonderful journey into the manufacturing, construction or industrial world, congratulations! You have chosen well. However, understanding the various components of this world can be overwhelming. Nevertheless, it is crucial for you to understand everything from the basics. In that effort, we aim to educate you on the basics of fastener threads, an important aspect of fasteners without which the aforementioned industries would not survive.

A screw thread is a collection of ridges in the form of a helix on the internal or external face of the fastener. Internally threaded fasteners are nuts while externally threaded ones are volts, screws or studs. Here, we will discuss thread series and what differentiates each type.

Fine and Coarse Thread Types

The most common thread types are UNC (Unified coarse pitch threads) and UNF (Unified fine pitch threads). As the name suggests, coarse threads come with a flatter thread top while finer threads are more pointed and better suited for dimensionally accurate applications.

Here are a few key points to remember about fine threads:

  • Fine thread bolts can handle increased tension due to their large stress areas.
  • They come with improved torsional and transverse shear strengths as a result of their large ‘minor’ diameter.
  • Compared to coarsely threaded fasteners, they are better are tapping into thin-walled surfaces.
  • Since finer threads come with a relatively small helix angle, they make for better contenders when it comes to adjustment accuracy.

Similarly, here are a few key points to keep in mind when it comes to coarse threads.

  • Compared to finer threads, coarse threads have a greater stripping strength for the same length of engagement due to its better hold of the surface.
  • It also comes with greater fatigue resistance.
  • Since the root gap between each thread is greater, it is less likely to cross thread.
  • Since coarse threads provide enough wiggle room when it comes to dimensional accuracy, it can also be easily assembled and reassembled.
  • Coarse threads also allow for better penetration into brittle materials.
  • It is also easier to coat and plate coarse threads compared to finer threads.
  • Automated manufacturing processes can be more efficient if coarse threads are used instead of fine threads.

Apart from UNF and UNC, there are a few more thread types that you should keep an eye out for.

UNR Threads

The only difference between UNR and the other UN type threads is the root radius which comes with a limit of 0.108-0.144 times the thread pitch. Today, all roll-threaded fasteners are of the UNR type since the die used to make the rounded crests have become the standard method for manufacturing most threads.

UNJ Threads

UNJ type threads come with a root radius which is 0.150-0.180 times the thread pitch. This larger radii cause the minor diameter of the thread to increase and intrude beyond the basic profile of the UNF, UNC, and UNR threads. However, to reduce the possibility of thread interference between mating threads, the minor diameter of the UNJ threads are increased. The standard tolerances for UNJ threads are 3A and 3B.

At ITA Fasteners, we are adept at understanding all your fastening requirements to ensure that the thread type you choose conforms to the right dimensional and material standard required by your application. For this reason, we are one of the best fastener manufacturers from around the world. For more about thread types and consultation for all your fastener requirements, do get in touch with us at sales@itafasteners.com

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