Understanding Thread Types for Fasteners
At Fastenright Ltd., we offer a wide selection of thread types for all kinds of fasteners, with some being more popular in certain regions than others. Knowing the thread type you require is crucial, as different threads serve distinct purposes.
Common Thread Types: Metric, UNC, UNF, BA and BSF.
Metric Thread
Metric threads are the most commonly used worldwide and are also known as ‘ISO Metric threads’ or simply ‘M’ threads. Both coarse and fine thread options are available in a wide range of materials and sizes, conforming to various popular DIN standards.
Choosing Between Fine and Coarse Metric Threads
- Fine Metric Threads:
- More prone to galling.
- Require longer thread engagement.
- Less suitable for high-speed assembly.
- Easier to tap into hard materials with lower torque requirements.
- Less likely to loosen and stronger than coarse threads of the same size.
- Ideal for applications requiring finer adjustments due to smaller pitch.
- Coarse Metric Threads:
- Feature a larger pitch.
- Easier to source and more commonly specified.
- Suitable for the majority of general-purpose applications.
Metric threads come in different strength grades, typically ranging from 4.8, to 8.8, 10.9 and 12.9, depending on the application’s requirements.
Metric Thread Applications
Metric threads are used in a wide variety of industries, including:
- Automotive: Fastening components in cars, trucks, and other vehicles.
- Construction: Used in structural fasteners and heavy machinery.
- Electronics: Securing components in devices and electrical enclosures.
UNC Thread (Unified Coarse Thread)
UNC stands for ‘Unified Coarse’ and is widely used in the United States. UNC threads are commonly found in the agricultural industry, where strong, coarse threads are preferred.
UNC Threads are part of the Unified Thread Standard (UTS) currently controlled by ASME (American Society of Mechanical Engineers) / ANSI (American National Standards Institute) in the United States. The UTS defines a standard thread series. It has the same 60° profile as the ISO metric thread, but the characteristic dimensions of each UTS thread (outer diameter and pitch) were chosen as an inch fraction rather than a millimeter value. A UNC thread has a larger pitch, fewer threads per inch, and a lower thread density compared to the UNF thread (below).
Key features of UNC threads:
- Deeper and more generic than fine threads.
- Easy to remove.
- Offer higher tolerance for manufacturing and plating processes.
UNC Thread Applications
UNC threads are particularly suitable for:
- Construction: Frequently used in wood and metal fasteners for building structures.
- Heavy machinery: Ideal for bolts that need to withstand high stress and vibrations.
- Maintenance and repair: Preferred for applications where frequent disassembly is required.
UNF Thread (Unified Fine Thread)
UNF stands for ‘Unified Fine’ and is another popular thread type in the United States. UNF Threads are also part of the Unified Thread Standard (UTS). UNF threads have a smaller pitch, more threads per inch, and a higher thread density. They are extensively used in the automotive and aerospace sectors, where fine threads are required for precision and tight fits.
Key characteristics of UNF threads:
- Typically made from steel or stainless steel.
- Provide better torque locking and load-bearing capacity than UNC threads.
- Offer a more specific fit and tighter tolerance.
UNF Thread Applications
UNF threads are generally suitable for:
- Aerospace: Used in aircraft components where precision and strength are crucial.
- Automotive: Commonly found in engines and other high-performance parts.
- Military: Preferred for fasteners used in defence equipment due to high reliability.
BA Thread (British Association Thread)
BA threads, also known as ‘British Association’ threads, are an older style British standard with numbered diameters. This thread type has been in use since 1884 and was standardised in 1903.
Although it is being gradually phased out in favour of metric threads, BA threads are still found in:
- Electrical fittings.
- Small screws.
BA threads are typically used in small precision instruments so may be used in legacy equipment, particularly in older scientific and optical devices.
BSF Thread (British Standard Fine Thread)
BSF, or ‘British Standard Fine’ thread is another older style British thread type, commonly used in vintage automobiles and machinery. Available in both steel and stainless steel, BSF threads are a fine-pitch alternative to other thread types.
Bolts, nuts, screws and other fasteners can all be seen with BSF threads and used in restoration projects. Often used by enthusiasts and specialists in heritage engineering, BSF threads are still in demand for restoring vintage cars and machinery.
Need Fasteners with Specific Thread Types?
At Fastenright Ltd., we can supply fasteners with any of the above thread types, customised to meet your specific requirements. Whether you need metric, UNC, UNF, BA, or BSF fasteners, our team is ready to assist with high-quality products tailored to your needs.
