What is 'AF'?

[Simpo Two]

I was looking for brass hex bar and 'AF' came up a lot.

I chose 4mm AF (8BA/5/32"). I know BA, but what does AF stand for?

[Richard-D]

Across Flats. It's a straight measurement between the two faces. Usually used with imperial sizes but correct with metric too.

[Simpo Two]

Perfect, thanks!

It looks like a kind of thread, like 'something Fine', but hex bar isn't threaded.

[Mercdriver]

Buy a set of Zeus charts, that will explain all- and a lot more!

[Baldchap]

It's 1972.

Like imperial measurements, unless you need it you don't need it and it absolutely should not be encouraged.

[littleredrooster]

It can either mean Across the Flats (hex bar, nuts etc.), or American Fine (screw thread) depending on the context.

[Simpo Two]

Baldchap said:

It's 1972.

Like imperial measurements, unless you need it you don't need it and it absolutely should not be encouraged.

In this case the size was crucial as it's for a scale model boat.

After a moment's thought I figured out that '1972' is not the year AF was invented but 0.1972". However that's 5mm not 4mm...

[Mercdriver]

Baldchap said:

It's 1972.

Like imperial measurements, unless you need it you don't need it and it absolutely should not be encouraged.

Rubbish!

[Baldchap]

I'll double down and say Whitworth too!

Metric is, thankfully, here to stay!

[OutInTheShed]

littleredrooster said:

It can either mean Across the Flats (hex bar, nuts etc.), or American Fine (screw thread) depending on the context.

Never heard of 'American fine'.
AF spanners are marked with the jaw size.
Whitworth spanners are marked with the bolt rod diameter.

'American' threads would be UNC and UNF, unified national coarse or fine.
Before the SAE unified standard threads, various companies used various threads.

I suppose it's always worth considering other people may have crackpot (to you!) understandings of obvious abbreviations.
I've had to ask UK engineers not to use 'mil' as short for 'mm', because in the US&A, a 'mil' is what my Dad used to call a 'thou'.
When it's not an angle, that is!

[Simpo Two]

Baldchap said:

I'll double down and say Whitworth too!

Metric is, thankfully, here to stay!

Just 'cos you couldn't do fractions at skool

We were much more successful as a nation when we used our own measurements. Then we adopted Napoleon's measurements and went the same way he did...!

[The Three D Mucketeer]

Baldchap said:

I'll double down and say Whitworth too!

Metric is, thankfully, here to stay!

You should tell American aircraft manufacturers that

[Sheepshanks]

OutInTheShed said:

I've had to ask UK engineers not to use 'mil' as short for 'mm', because in the US&A, a 'mil' is what my Dad used to call a 'thou'.

With 40x difference, that could lead to some head scratching depending on where the design was built!

[Mercdriver]

The large orbiting mirror had the wrong curvature because the yanks took the metric measurements as imperial.

1960/1970 American cars have ANF and ANC threads so if you are restoring a car from that generation Zeus charts will help you find the proper thread.

[BrokenSkunk]

OutInTheShed said:

I've had to ask UK engineers not to use 'mil' as short for 'mm', because in the US&A, a 'mil' is what my Dad used to call a 'thou'.

For the same reason I spent a coule of decades asking the Americans to use "thou" instead of "mil", 'cus it confused the UK team.

[popegregory]

As an aside to the previous helpful answers, don’t use it in conversation with a young person…

[Mercdriver]

No point in discussing the different threads used by bicycle manufactures then, they used another system altogether

[ARHarh]

Mercdriver said:

No point in discussing the different threads used by bicycle manufactures then, they used another system altogether

It was all 26 tpi if I recall though so you only needed one thread gauge

[Error_404_Username_not_found]

Imperial (or inch based) measurement and thread standards seem to have survived quite well, even outside USA, in hydraulic/pneumatic applications.
BSPP, BSPT, NPT, JIC, and so forth. Even then the American style fittings stick to established SAE thread forms. JIC connectors use UNF threads IIRC. And even Swagelok which is relatively modern is inch-based.
This got some of my younger trainees a bit hot under the collar, not wanting to buy inch sized tools.
I'm aware there are metric hydraulic connections (Ermeto? and some weird Russian stuff), but I very seldom ever saw any.

See also: wheel and tyre sizes which blithely mix Inch and Metric!
I have also personally seen UNF threaded wheel studs and screws with metric hexes.

I still have the Whitworth/BSF spanners and sockets I bought around 60 years ago, and occasionally still get to use them.

[littleredrooster]

ARHarh said:

Mercdriver said:

No point in discussing the different threads used by bicycle manufactures then, they used another system altogether

It was all 26 tpi if I recall though so you only needed one thread gauge

It was indeed. BSA, AJS/Matchless, Triumph, Norton et al used to scatter Cycle Thread stuff around the bikes, alongside the usual BSF/BSW stuff.