Difference between fine and coarse threadfor steel

Perhaps the most recurring question you hear in the fastener manufacturing industry is whether a coarse thread bolt is better than a fine thread bolt. It’s a legitimate question, considering that coarse threads are stronger and have an overall greater resistance to cross-threading and stripping, while the fine thread fasteners have a slightly larger tensile […]

Perhaps the most recurring question you hear in the fastener manufacturing industry is whether a coarse thread bolt is better than a fine thread bolt. It's a legitimate question, considering that coarse threads are stronger and have an overall greater resistance to cross-threading and stripping, while the fine thread fasteners have a slightly larger tensile stress area. The short answer is that for general industrial applications, coarse thread bolts present several advantages over fine threads.

Coarsevsfine threadchart

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Difference between fine and coarse threadsizes

The only situation when fine thread bolts are preferable to coarse is in applications that require a larger tensile stress area. Other potential circumstances when using fine thread bolts makes sense include:

In the event that you need stainless steel fasteners for your application, then opt for coarse threads, as their chances to gall are lower. Galling occurs due to abnormal surface friction and the closer the fit between the mating threads, the more welded the nut will be. It is necessary to mention that minor galling can be very hard to detect sometimes. To put it simply, while a galled bolt has passed all quality tests and inspections, it will still not be able to function properly.

As an industry standard, the plating needed for course thread bolts is 20% higher than the one required by fine threads. In addition, due to their distinct manufacturing processes, the plating on fine threads tends to have more gagging and presents more assembly problems compared to coarse threads.

Difference between fine and coarse threadvscoarse thread

A typical coarse thread fastener of 3/8-16 inch can be installed almost 70% faster than its 3/8-24 fine thread counterpart, thus saving you time, money and energy. This feature makes them desirable fastening solutions for industries and applications where quick assembly and disassembly is required. Moreover, if the bolt gets damaged or is corroded, then it would be easier to replace, thus ensuring your equipment will be operational again in no time.

In applications where the length of the thread engagement is short, coarse threads are preferable due to their higher resistance to stripping. Innately, coarse threads have a greater height and hence, a larger volume of material between each lining compared to their fine counterparts. The extra height is typically around 33% for coarse threads, meaning there's considerably more material to resist stripping.

Because the gaps obtained in a fine thread bolt are shallower, it means that they are more likely to be distorted by a nick of a certain dimension. Nicking refers to the misalignments found in threads that can appear as a result of the manufacturing process or during transportation. While they can develop all along the surface of the bolt, the nicks on the first thread are usually the most problematic since they will make it increasingly difficult to properly fasten the bolt.