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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
    If only the first couple of threads are damaged then it might be the best choice to carefully ream them out. Once the damaged threads are removed then a bolt can be inserted into the hole which will engage with the remainder of the threads that are undamaged. There is probably no need to re-tap the hole if there are a sufficient number of undamaged threads remaining.
  • Former Community Member
    0 Former Community Member
    Andy,

    Can you say what make and model of milling machine this is?

    Someone may have access to a parts catalogue which may indicate the screws used.

    I have found this a lot with older machines when I used to have to repair them, the manuals can be useful to identify threads, even when a hundred miles away from them!!!

    I used to do so much I ended up with a full set of BSW & BSF taps.

    It was rare in my experience to find BA threads on anything other than electrical or automotive equipment.

    Machinery tended to be BSW/F on the mechanical bits.

    Your other option is to drill it out and "Helicoil"* it.

    That way you would know it is 3/16" BSF.

    Unless it is a liquid tight thread this may well be the easiest option, and there are ways around sorting it out if it's a liquid tight thread.


    You can by a kit with 10 1.5xD inserts for around 40 Euro direct from the manufacturer including tax & delivery to the UK.

    *Other manufacturers of wire thread inserts are available.
  • 0
    Mike, this is true but a combination of the cast you suggest and a thread gauge should work.

    Alasdair
  • 0
    I fear, as 2BA is about 4 or 5mm dia, and thread pitch 0.81mm  (0BA is practically M6, 6mm dia, and 1mm pitch, and each higher  BA size is 90% of the dimensions of the preceding.)

    You may not find it possible to get a gauge that is thin enough to fit down hole and engage sufficiently convincingly to be sure. Depending on the hole depth and the how much is damaged it may be safer to taper ream the damaged turns until a bolt fits. (and note that a brass bolt will reveal binding without damaging the steel, though go gently, you do not wish to snap the head off.)
  • 0
    Andy,

    Your best bet is probably to buy a set of thread gauges to check the thread (you may need to buy a set of BSF and a set of BA, but if you suspect it is BSF then that set will probably be all you need). You can then check the thread pitch as a thread gauge about 1" long should easily identify the difference. Granted it may be a one off expense that you only use once at £5-10 per set, but if it is what is needed to avoid wrecking an expensive piece of equipment may be justified.

    Alasdair
  • 0
    you wont tell on the diameters, as the tolerances will overlap. 2BA is large enough to take a 'cast' of the thread profile - a match stick and wax or soap or at a push blue-tac should do the trick, or depending how the threads are damaged a 'screw' from a plain brass rod coated in soft solder.

    There are 2 things,  all BA have a 47degree pitch angle, as opposed to 55 for whitworth and 60 for metrics and UNF,  so a look at the thread depth, and if the hole goes deep enough, then you may get something on TPI.
  • 0
    Now an even more challenging question for anyone: How do you determine whether an internal thread is 3/16 BSF (internal diameter 0.1475 inches, 32 TPI) or 2BA  (internal diameter 0.1467 inches, 31.4 TPI)? Now because that's far too easy ? I'll add that the first couple of threads are damaged so I can't just try a screw of each size in it - I'm going to need to buy a tap to "reform" the thread. And if it's the wrong one it will just completely destroy the rest of the thread.


    To be honest, since it's in a UK built milling machine from 1940s-1950s I'm 99.9% confident it will be BSF, but it will be very embarrassing if I get it wrong - I'm assuming that the steel's going to be pretty resistant to drilling out and retapping!


    Having finally got around to fitting a new chuck to my lathe which involved tapping a 3/4" BSF thread in the backplate I feel like I'm on a roll now - this milling machine's been just sitting there for about 15 years waiting for me to get around to replacing this tiny (but very vital) screw ?


    Cheers,


    Andy
  • 0

    Andy Millar:

    ...and given that no-one on eBay sells the UNC nuts I'm after in the UK anyway (I only need a handful), I'll try BSW and see what happens! Being brass screws they probably are BSW anyway. Brass screws do seem to be the last bastions of imperial threads in the UK, I guess because the threads tend to be coarser. Or because most of us who use brass fixings a lot tend to be terribly old smiley




    Are the cupboard door knobs American? 99.9% of things with UNC threads are American. If they are British then they will be Whitworth. There is some truth to what you say about the coarser threads in soft metals.


    Brass screws with UNC threads do exist but they are uncommon. Probably because of the American cost cutting culture. Titanium screws with UNC threads are quite common as they are used in aerospace.


  • 0
    ...and given that no-one on eBay sells the UNC nuts I'm after in the UK anyway (I only need a handful), I'll try BSW and see what happens! Being brass screws they probably are BSW anyway. Brass screws do seem to be the last bastions of imperial threads in the UK, I guess because the threads tend to be coarser. Or because most of us who use brass fixings a lot tend to be terribly old smiley


    Cheers,


    Andy
  • 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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