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UNC and UNF fasteners in Britain
Arran Cameron
436 Posts
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?
39 Replies
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
Roy Bowdler
820 Posts
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.        
 
Arran Cameron
436 Posts
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.
Paul Skyrme
151 Posts
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.
Andy Millar
1763 Posts
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
Arran Cameron
436 Posts
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.
Arran Cameron
436 Posts
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.
Andy Millar
1763 Posts
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
 
Paul Skyrme
151 Posts
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
Arran Cameron
436 Posts

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.

 
Andy Millar
1763 Posts
...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
Arran Cameron
436 Posts

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.

Andy Millar
1763 Posts
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
mapj1
3153 Posts
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.
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
mapj1
3153 Posts
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.)
Mike, this is true but a combination of the cast you suggest and a thread gauge should work.
Alasdair
Paul Skyrme
151 Posts
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.
Arran Cameron
436 Posts
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.
Andy Millar
1763 Posts
Sorry for the slow reply to all the excellent replies - I was trying to get work finished before holiday, and then I was being away on holiday 

Yes, I'd wondered about trying the matchstick (or toothpick) and wax / blue tac idea, the problem is that it is the hole is so small that might be challenging, particularly given the tiny difference in thread pitch I'm trying to measure. 

The manufacturer is something like "Tew & Sautkey" - it's cast in under a layer of thick enamelling so not easy to make out. I can't find a reference to them (or any name like that) anywhere, if this rings any bells with anyone it would be very interesting to know.

I'll get hold of a 3/16 BSF screw (I've already got loads of 2BAs) and have a play - I might try gently grinding down the first couple of damaged threads with a cone shaped grinder in a Dremel. If nothing else that'll give me a clue as to how hard this bit of steel is.

But I will get myself a set of imperial thread gauges anyway when a nice set comes up on eBay etc...I've also just had to work out what the thread is on the drawbar for the chuck so I can buy some new collet chucks, but as that was 3/8" BSW that was easy - (relatively) big and chunky!

Cheers,

Andy
Roger Bryant
290 Posts
Have you tried the  http://www.lathes.co.uk/   site? Depending how illegible the name is could Midgley & Sutcliffe be an option? 

Best regards

Roger 
 
Andy Millar
1763 Posts
The "Tew" bit is definitely right, it's the second name where some of the letters are blurred, but the number of letters is right.

Yes, I've been using lathes.co.uk to find the history of my lathe (cracking site), it's on this page http://www.lathes.co.uk/portass/index.html in the 1939 advert some way down as the "Super £7.19.6"! But isn't featured anywhere else on his site so I might send him some photos.

Cheers,

Andy



 
Andy,
One thing that has occurred to me is that if it is only the first two or three threads that are damaged it may be practical to run a plug tap a couple of turns into the hole and it may not matter whether you use 3/16 BSF or 2BA as the difference between the two is not major. Of course this is assuming that the damaged threads are a small proportion of the total length of thread. My guess would be you are dealing with BSF as you suspect, but being a slightly smaller diameter (both at thread top and bottom) the BA tap might be safe as a first try even if it turns out to be BSF. Sadly though I used to have my father's old BA tap and die set, it vanished during a move (I think in the direction of my brother....).
Andy Millar
1763 Posts
Hi Roger,
As it turns out they were on lathes.co.uk after all, while I was looking there again I just found them by chance hidden under "Rodney"!!!
"Made by Tew & Gautrey in Church Street, Gogenhow, Northamptonshire"
So I was close with the name.

One like mine is at the bottom of http://www.lathes.co.uk/rodney/ with photos captioned (my underline) "The seldom-found, stand-alone Rodney vertical miller"

That's satisfying! And, because it was more commonly sold as an attachment for Myford lathes, if I do get really stuck there's probably someone in the Myford fan club who'll be able to help.

Cheers,

Andy
 
Roger Bryant
290 Posts

So half the problem solved 😀 I think that trying to remove the damaged threads is the best solution. They were probably damaged by someone trying to use the wrong thread, possibly metric ☹

When you have got your machines in good working order here's a project suggestion: A breath powered piston valve engine, 6mm bore.

26bcc62cefae1506dd43de98fbf50dee-huge-ds

https://youtu.be/qoLbLisxNLU

It's good as an icebreaker when starting to talk about engineering, just take it out of your pocket and give a blow (it also doesn't smell like my IC models do)

Best regards

Roger

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