Which is stronger: UNC or UNF Thread? Why?


UNC vs UNF Threads

What is a thread system?

A thread system is a set of various designations intended to represent the different sizes, which in turn is used to define the thread geometry. Of the two major screw thread systems, the Unified Screw Thread System is used across the United States and Canada. Two of the commonly used Unified form thread designations have been represented by abbreviations such as UNC as well as UNF.

What are UNF Threads and UNC Threads?

Both the UNF and UNC are two symbols that are a part of the Unified Screw Thread Series. The definition of these two symbols is based on the number of threads per inch as well as the standardized with a gauge. UNF threads are known as Unified fine pitch threads, whereas UNC threads are known as Unified coarse pitch threads. While screws from both the UNF and UNC thread are used for fastening, the application of these screws varies in different fields.  For instance, UNF threaded screws have a breaking load capacity that is slightly higher as compared to UNC threads due to their lesser thread depth. And the Unified National Fine has a larger tensile stress area, meant to be used for gages that have an identical material as well as diameter. On the other hand, UNC is the more popular one amongst the two due to many buyers preferring this thread for general application inch gaging. As a consequence of its inherent coarse pitch, the threads of the Unified National Coarse tend to be deeper in comparison to fine threads. Hence, the UNC threads provide for an easier assembly minus cross threading.

What is the difference between UNF and UNC thread?

The preloads of both UNF as well as UNC threads are close when they are used as fasteners. In terms of preventing the effect of loosing of a fine thread is better in contrast to that of a coarse. In instances when a fine thread screw is used for adjustment, it offers more advantages.

The UNF threads are produced with a smaller helix angle along with better tightness. Hence, the UNF threaded screw is more conducive to the self-locking of the thread. Therefore, it is not that easy to loosen a UNF as compared with UNC threads. Which is why UNF threads are typically used for parts that are thinly walled as well as for equipment that has a higher anti-vibration requirement. Since UNF screws have a smaller pitch, there are a higher number of teeth that are screwed in the same length. This higher number of teeth aids in the reduction of fluid leakage, so it is advantageous to be used for those applications where sealing is needed. In opposition, a UNC threaded screw is manufactured with a less number of teeth on the same length. However, the size of each tooth in UNC threads has a larger cross-section, thus proving to be well suited for applications in that are to bear larger tensile force and impact force.  Juxtapose to a fine screw thread, a coarse screw thread will exhibit higher strength in addition to good interchangeability. Moreover, a UNC threaded screw also has greater tolerances and gas the ability to handles manufacturing and plating in a much better manner contrast to the UNF threaded screw. Due to the aforementioned varying features, both the Unified coarse screw threads and the Unified fine screw threads have different uses.

Application of UNC threads

Because of its unique advantages in some rough operation applications, the UNC is used in mass production of threaded fasteners, for instance, bolts, screws, nuts, etc. These applications not only require quick assembly or disassembly but also resistance to both corrosion and damage.

Application of UNF threads

The smaller pitch of the UNF thread with the same nominal specification, higher thread strength, along with smaller space occupation size is what gives it better self-locking performance. Therefore UNF is mainly used for adjustment, positioning or fixation and for fine adjustment.

Which thread is stronger?

Speaking of UNF, the height of the fine thread is smaller, which is why it is easy to get disordered during installation. Hence it is not able to bear a larger load as compared to UNC threaded screws. Contrary to UNF threads, the threads of a UNC screw are much higher, resulting in higher load-bearing capacities due to its strength.