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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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    Purely from memory of the mid to late 70s, especially my first year which included C&G Basic Engineering Craft Studies (Mechanical) and was shared by apprentices of CEGB (me), Jaguar, Metro-Cammell and other employers around “the workshop of the world”. Metric units were used in the machine shop and hand fitting, with an occasional imperial dimensions exercise, but most equipment had imperial threads (BSW or BSF). AF ("American Fine") was regularly mentioned as being common in the motor industry. AF was also I think used to describe spanners, bolt heads and nuts (“across the flats”). BA was the standard for small electrical and instrumentation, motor terminal connections and the like.  I carried OBA, 2BA and 4BA spinners and spanners. I still have a hoard of BA screws & bolts and possibly a tap & die or two in my shed somewhere. As Alasdair mentioned, tables and gauges were available for unusual/ critical situations, although it wasn’t unusual to find a “bodge” with a damaged thread and weakened connection. I didn’t gain any experience of shipbuilding or construction at that time. The situation changed very slowly during my 20 years in the electricity supply industry ,since the overwhelming majority of the equipment was procured before 1970 and much of the post war infrastructure, built to last as it was (e.g. Reyrolle JW420) is still in use.        

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    Purely from memory of the mid to late 70s, especially my first year which included C&G Basic Engineering Craft Studies (Mechanical) and was shared by apprentices of CEGB (me), Jaguar, Metro-Cammell and other employers around “the workshop of the world”. Metric units were used in the machine shop and hand fitting, with an occasional imperial dimensions exercise, but most equipment had imperial threads (BSW or BSF). AF ("American Fine") was regularly mentioned as being common in the motor industry. AF was also I think used to describe spanners, bolt heads and nuts (“across the flats”). BA was the standard for small electrical and instrumentation, motor terminal connections and the like.  I carried OBA, 2BA and 4BA spinners and spanners. I still have a hoard of BA screws & bolts and possibly a tap & die or two in my shed somewhere. As Alasdair mentioned, tables and gauges were available for unusual/ critical situations, although it wasn’t unusual to find a “bodge” with a damaged thread and weakened connection. I didn’t gain any experience of shipbuilding or construction at that time. The situation changed very slowly during my 20 years in the electricity supply industry ,since the overwhelming majority of the equipment was procured before 1970 and much of the post war infrastructure, built to last as it was (e.g. Reyrolle JW420) is still in use.        

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