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?

I have read this whole thread with great interest.


 If Whitworth and BSF became officially obsolete in 1948, then my observations suggest that many industries ignored officialdom. This is possibly just as well. Many industries in the 1950s probably had the foresight to recognise that the standard used in countries where the metric system was well established - the standard now known as Isometric - was the "band waggon". A planned and phased move to that standard when the  time was ripe was preferable to converting to American standards with the prospect of a further conversion later.


To answer the initial questions:


1.  I served my time in the 1960s in the electricity supply industry. There, Whitworth and BSF were dominant and in continuing use by plant manufacturers.  I came across American Unified fasteners mainly on motor cars. At the time I put this down to the dominance of American organisations like Ford and GM. Ford was later a key player in the automotive industry's conversion to Isometric.


2. I believe that the smallest Whitworth size was 1/8 inch. I came across this size in domestic appliances but it was rarely found in the industrial environment, where the BA series was more popular for fasteners of this size. Whitworth sizes were popular from 3/16 inch upwards.


3. I have little experience of the construction industry at that time. On theatre electrical equipment, I came across both UNC and Whitworth. This caused confusion because the two standards were similar but not quite identical. A nut of one could sometimes be forced onto a screw thread of the other - not recommended practice of course. Confusion was further caused by the nut sizes (across the flats) being different.


4. I have long thought that a lot of obsolete stuff, surplus to industry's requirement, gets dumped on the home DIY market. The move from Whitworth to Isometric was somewhat sporadic, with Unified occasionally getting in the way. I remember once around 1975 in a hardware store, asking for some Isometric fasteners, and being told, rather pompously, "They will never catch on for years yet." Six months later, the  same shop was selling almost exclusively Isometric

• Quote

Re: UNC and UNF fasteners in Britain

Posted by mapj1 on Jun 5, 2019 4:09 pm

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.)

regards Mike

As others have pointed out, the BA range was essentially metric based. 0BA is practically the same as M6 with a thread pitch of 1 mm but the thread profile is different. Other BA sizes do not have such clear round dimensions, though there is a logical system. I think one reason why BA did not catch on is because people prefer, to gauge numbers, sizes relating to actual physical dimensions in recognised measurement units, so that bolts can be easily related to bolt hole clearances, etc. To give a parallel example, the gauge sizes for self-tapping wood screws had a good purpose in the mid-20th century, but nowadays the actual thickness in millimetres is preferred. I remember a fiasco in the mid 60s when fitters requested the factory store to issue some sheet metal. Their request was in actual thickness as measured with a micrometer, but the storeman only knew gauge numbers. Two hours were wasted until someone found a conversion chart.


I recently required some 4BA screws for an electrical job. The nearest to this you can buy in shops nowadays is M3·5. I got what I wanted from E-bay without difficulty.

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?

I have read this whole thread with great interest.


 If Whitworth and BSF became officially obsolete in 1948, then my observations suggest that many industries ignored officialdom. This is possibly just as well. Many industries in the 1950s probably had the foresight to recognise that the standard used in countries where the metric system was well established - the standard now known as Isometric - was the "band waggon". A planned and phased move to that standard when the  time was ripe was preferable to converting to American standards with the prospect of a further conversion later.


To answer the initial questions:


1.  I served my time in the 1960s in the electricity supply industry. There, Whitworth and BSF were dominant and in continuing use by plant manufacturers.  I came across American Unified fasteners mainly on motor cars. At the time I put this down to the dominance of American organisations like Ford and GM. Ford was later a key player in the automotive industry's conversion to Isometric.


2. I believe that the smallest Whitworth size was 1/8 inch. I came across this size in domestic appliances but it was rarely found in the industrial environment, where the BA series was more popular for fasteners of this size. Whitworth sizes were popular from 3/16 inch upwards.


3. I have little experience of the construction industry at that time. On theatre electrical equipment, I came across both UNC and Whitworth. This caused confusion because the two standards were similar but not quite identical. A nut of one could sometimes be forced onto a screw thread of the other - not recommended practice of course. Confusion was further caused by the nut sizes (across the flats) being different.


4. I have long thought that a lot of obsolete stuff, surplus to industry's requirement, gets dumped on the home DIY market. The move from Whitworth to Isometric was somewhat sporadic, with Unified occasionally getting in the way. I remember once around 1975 in a hardware store, asking for some Isometric fasteners, and being told, rather pompously, "They will never catch on for years yet." Six months later, the  same shop was selling almost exclusively Isometric

• Quote

Re: UNC and UNF fasteners in Britain

Posted by mapj1 on Jun 5, 2019 4:09 pm

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.)

regards Mike

As others have pointed out, the BA range was essentially metric based. 0BA is practically the same as M6 with a thread pitch of 1 mm but the thread profile is different. Other BA sizes do not have such clear round dimensions, though there is a logical system. I think one reason why BA did not catch on is because people prefer, to gauge numbers, sizes relating to actual physical dimensions in recognised measurement units, so that bolts can be easily related to bolt hole clearances, etc. To give a parallel example, the gauge sizes for self-tapping wood screws had a good purpose in the mid-20th century, but nowadays the actual thickness in millimetres is preferred. I remember a fiasco in the mid 60s when fitters requested the factory store to issue some sheet metal. Their request was in actual thickness as measured with a micrometer, but the storeman only knew gauge numbers. Two hours were wasted until someone found a conversion chart.


I recently required some 4BA screws for an electrical job. The nearest to this you can buy in shops nowadays is M3·5. I got what I wanted from E-bay without difficulty.