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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?
  • 0
    Arran,

    I can't give a definite answer but my memory from shipbuilding is that shipyards moved across to metric measurements in the late '70s (with one example I remember at Scott Lithgow in Port Glasgow "We need another section of cable tray for here, 300mm by 6 feet") but my memory was that this was a transition from BS Whitworth. As I didn't experience any UK built ships built between 1960 and 1979 I can't be sure there wasn't an intervening period of UNC/UNF.

    By the way, BA was actually a metric thread standard but it didn't really catch on elsewhere so I think it was assumed to be imperial by most people. However I don't recall seeing it used anywhere.

    On availability, certainly when I was buying my first tools in the late '70s and early '80s metric was readily available, but when faced with an existing bolt, thread guages were a necessity as there were so many different possible options that you needed to have bolt diameter and thread pitch in order to look up what you were faced with. I seem to remember that it was possible to buy the right nuts and bolts, but that is not the same as it was easy to do so.

    I may have some old bits and pieces at home to help here so if I am able to look them out I may be able to add some more info.

    Alasdair
  • 0
    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.        

  • 0
    According to the 1965 Halfords catalogue

    https://classics.honestjohn.co.uk/halfords-1965-catalogue/


    Set pins and nuts are available individually in BSF sizes. Round headed screws with hexagon locking nuts in 2BA size. Also a Halfords Handyman Assortment. 36 UNF bolts and nuts, suitable for BMC, Ford, and Vauxhall cars etc. Sizes 5/16” × ½” to 5/16” × 1½”. Packaged in attractive tin. Keep one in your garage. Price 9 shillings. No mention of any metric fasteners.


    The spanners listed are Whitworth or AF although it does say in the small print that Gordon spanners are available in metric. These are highly prized today as Gordon was the Snap-On of the 1960s. The socket sets by Halfords, Britool, and Swinborne are all Whitworth or AF.


    UNC fasteners are commonly encountered in medical devices designed or manufactured in the US. They tend to be the smaller numbered sizes although sometimes sizes ¼ inch or larger are encountered on stands and mounting brackets. It can be tricky to source replacements this side of the Atlantic. Just ask anybody who services medical devices. They often keep a stock of fasteners salvaged from scrapped medical devices as a result.


    I was verbally informed that 1960s tower blocks were held together with whatever fasteners were the cheapest at the time which, more often than not, would have been Whitworth.
  • Former Community Member
    0 Former Community Member
    Don't forget, unless you are doing something really special, high performance or high stress, BSW & UNC are interchangeable in the fractional sizes all apart from 1/2", even if it's a temporary fix whilst you order the right fasteners.

    UNC, UNF, BSF, BSW, & BA are all still available in the UK, not necessarily from stock, though we do have a very good supplier locally who does have a very good stock, one of the national catalogue supppliers for sure still keeps them, and in small quantities if you want them.
  • 0
    Hi,

    I remember coming across UNC and UNF really quite late (in the 80s, possibly 90s) which suggests they weren't around in the company - a good old UK engineering company - where I did my apprenticeship in the late 70s. From memory, and I may be wrong, they mostly used BSF for heavy work, but might have been Whitworth. Definitely, as Roy says, BA sizes were used everywhere in electronics in the 70s - only about 5 years ago we were still using them in railway signalling products much to the annoyance of our suppliers.


    BA are also still used on Mamod steam engines, luckily I have plenty of BA spanners lying around from the old days!


    Cheers,

    Andy
  • 0
    BA fasteners were used in British Strowger telephone exchanges, with larger sizes in BSF, but the mechanical dimensions of the equipment were standardised in the 1930s so it was not feasible to use UNC and UNF fasteners on equipment manufactured after 1948.


    UNC and UNF fasteners were used on Rootes cars as Chrysler took over the company in the 1960s. Cars later manufactured in Iran often use metric fasteners or in some cases UNC and UNF fasteners with metric size heads as AF spanners are difficult to find in Iran.
  • 0
    There was once the mystery as to which family of spanners were required to work on a Raleigh Burner BMX. Take into account that in the early 1980s there were many times more Whitworth and AF spanners in toolboxes than there are today. The answers were published in an article in a school magazine from the era.
  • 0
    Here's a bank holiday question for anyone: How do you tell whether you have a #10 UNC screw or a 3/16" Whitworth screw using normal measuring aids??? (i.e. I haven't got a thread profile gauge! I do have micrometers.) As far as I can tell from a web search they're very nearly identical except for the thread profile.


    A rhetorical question is why the manufacturer of these brand new cupboard door knobs didn't use M5 screws smiley Although they came with nuts I want to buy some T nuts to use instead for neatness.


    Cheers,


    Andy

  • Former Community Member
    0 Former Community Member
    I don’t think that you can Andy.


    Just use whichever one you can get.

     I have done that switch several times on UNC & BSW both ways, there’s normally enough clearance in the thread.

     I have even done it on paying jobs, as long as the fasteners are not under high load.


    Paul
  • 0

    Andy Millar:

    Here's a bank holiday question for anyone: How do you tell whether you have a #10 UNC screw or a 3/16" Whitworth screw using normal measuring aids??? (i.e. I haven't got a thread profile gauge! I do have micrometers.) As far as I can tell from a web search they're very nearly identical except for the thread profile.




    Close examination will reveal that the Whitworth has rounded crests on the thread whereas the UNC is flatter. They will mate reasonably well as they are both 24TPI.




    A rhetorical question is why the manufacturer of these brand new cupboard door knobs didn't use M5 screws smiley Although they came with nuts I want to buy some T nuts to use instead for neatness.




    Many companies haven't gone metric yet.



     

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