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UNC and UNF fasteners in Britain

Arran Cameron
Somebody will know the answer to this…


Almost all British machinery manufactured before 1950 used Whitworth, BSF, or BA fasteners. Manufacturers moved towards using metric fasteners in the 1970s and these have been the most commonly available and used family since 1980, although the proposal to use metric fasteners dates back 1965. Whitworth and BSF officially became obsolete in 1948 following an agreement between the UK, US, and Canada to standardise on the American UNC and UNF fasteners for future use. UNC and UNF fasteners were used in British machinery manufactured in the 1950s, 60s, and 70s where they gradually replaced Whitworth and BSF before themselves being replaced by metric fasteners.


1. Were UNC and UNF fasteners used across most industries in the UK or were they largely confined to specific industries such as automotive and machine tools? Were they regularly used in railways or shipbuilding?

2. Were the numbered sizes smaller than ¼ inch commonly used or did industry stick with BA fasteners until they moved to using metric fasteners?

3. Were UNC and UNF fasteners commonly used in construction? What are the most common family of fasteners used to hold together 1960s tower blocks and university buildings?

4. Was it easy to buy UNC and UNF fasteners from hardware and DIY shops in the 1960s and 70s or did they move directly from selling Whitworth and BA fasteners to metric fasteners?
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  • 0
    In the 1960s bicycles were a bit of a mixture of thread types. BA seemed to be used for some of the smaller bolts, e.g. fixing mudguard stays to frame. The system was also slightly confused by the similarity of BSC to BSF in some sizes. I once had to replace a lost bolt on a prop-stand, and I used a 1/4 inch BSF one, easy to obtain. I "cleaned up" the thread with a  tap and it fitted OK. In reality it was probably a replacement for a BSC bolt. Both BSC and BSF 1/4 inch are 26 threads per inch, with a slight difference in thread profile. Indeed these are very similar to 0BA and M6, which have thread pitches of 1 mm or 25·4 threads per inch. I read somewhere that one type will screw onto the other provided the threaded section is not too long.


    I believe that the British Cycle threads are still used on "cycle specific" parts, such as threads associated with bearings, for which the fine thread form is highly suitable.
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  • 0
    In the 1960s bicycles were a bit of a mixture of thread types. BA seemed to be used for some of the smaller bolts, e.g. fixing mudguard stays to frame. The system was also slightly confused by the similarity of BSC to BSF in some sizes. I once had to replace a lost bolt on a prop-stand, and I used a 1/4 inch BSF one, easy to obtain. I "cleaned up" the thread with a  tap and it fitted OK. In reality it was probably a replacement for a BSC bolt. Both BSC and BSF 1/4 inch are 26 threads per inch, with a slight difference in thread profile. Indeed these are very similar to 0BA and M6, which have thread pitches of 1 mm or 25·4 threads per inch. I read somewhere that one type will screw onto the other provided the threaded section is not too long.


    I believe that the British Cycle threads are still used on "cycle specific" parts, such as threads associated with bearings, for which the fine thread form is highly suitable.
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