Why You Should Choose Coarse Thread Bolts Over Fine Thread Ones
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.
- Higher resistance to stripping
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.
- They are less affected by thread nicking
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.
- They are less likely to gall
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.
- They are easier and faster to assemble
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.
- They are less affected by plating build-up
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.
Fine thread bolts can be employed in industrial applications
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:
- The fastener will be constantly exposed to vibration
- You need fine and very precise adjustments
- The application requires less tapping torque
About the Author
Started my career in the fastener world in 1969 at, Parker Kalon Corp. a NJ based screw manufacturer located in Clifton, NJ working in inventory control, scheduling secondary production and concluding there in purchasing. In 1971 I accepted a sales position at Star Stainless Screw Co., Totowa, NJ working in inside sales and later as an outside salesman, having a successful career at Star I had the desire with a friend to start our own fastener distribution company in 1980 named: Divspec, Kenilworth, NJ. This was a successful adventure but ended in 1985 with me starting Melfast in August 1985 and have stayed competitive and successful to date. Melfast serves the OEM market with approximately 400 accounts nationally.
