The 8UN and UNC thread series are both part of the Unified Thread Standard, used primarily in the United States and Canada. However, they have distinct characteristics and applications:
- TPI (Threads Per Inch):
- 8UN: This designation indicates the series has 8 threads per inch. It is typically used for larger diameters and where a coarse thread is more advantageous, e.g., when the material into which the thread is cut is not very strong.
- UNC (Unified National Coarse): UNC is the most common coarse thread series with a variable TPI based on the diameter of the screw or bolt. It is more general-purpose and used across a wide range of applications.
- Diameter:
- 8UN: Generally used for larger diameters where the strength and ease of thread engagement/disengagement are factors.
- UNC: Can be used for a variety of diameters, from small screws to large bolts.
- Strength and Material Tensile Strength:
- 8UN: The coarse 8 TPI is suitable for low tensile materials but also provides high-strength fastening in large diameter bolts.
- UNC: It’s a versatile series that offers a balance between thread strength and good shear resistance while being easier to tap and less prone to cross-threading than finer threads.
- Application:
- 8UN: Often seen in heavy machinery and construction where the loads are heavy and a robust thread is needed. It’s also used in applications requiring frequent assembly and disassembly.
- UNC: Broad use across general industrial, consumer products, and construction. They are standard for many typical fasteners and are chosen for ease of use and availability.
- Compatibility:
- 8UN: Due to its specific use cases, it may not be as commonly available as UNC, and compatibility with other equipment requires more careful consideration.
- UNC: Being a more universal thread series, UNC fasteners are widely compatible with products manufactured in or exported to the USA and Canada.
In summary, the 8UN series is a specialized thread type with a constant 8 TPI that’s often associated with larger diameters and high-strength requirements, while the UNC series encompasses a range of thread coarseness across various diameters and is used for a wide variety of everyday applications.
