AF hex?

I just want to know what AF means. I read in an instruction that the part is made from 4mm AF hex?

I've always understood AF to mean 'Across Flats', but I stand to be corrected by those with a greater knowledge than mine!

Andy

Axel,

It simply means 'across flats'.....the distance between 2 parallel sides.so in your case you need some hex bar that is 4mm across from one flat face to opposing one....

Its as simple as that......

Thanks too all, I just figured it out myslef actually! (Not too stupid after all!)

A sure candidate for the proposed Glossary

Cheers, Tim

As we are on the subject of 'across flats' does anyone know how the rather odd Whitworth hexagon sizes came about . I genuinely don't know but I do know 2 things 1/ whit head sizes were reduced in the war to the 'next size down' bsf sized hexagons. 2/ whit BSF hex sizes match neither metric or imperial ' whole' sizes , so for example 5/16 bsf has a hex size a little bigger than 1/2" but bigger than 13mm, but smaller than 14mm or 9/16.

I'm unsure why BSW spanners are the sizes they are but in trying to find an answer I came across this at http://www.sat.dundee.ac.uk/psc/spanner_jaw.html

"It is a common view that the odd Whitworth/BS spanner sizes are 'illogical' and that the newer metric system is much more 'logical', but consider this: To cover 1/4" to 3/4" in both fine (BSF) and coarse (BSW) threads, the British system defines 9 diameters and requires 9 spanners (or 10 if you also include the original large head Whitworth sizes as well). The UNF/UNC system defines 8 diameters for the same range but requires 11 spanners. For the broadly equivalent range in metric of M6 to M18 using all the common metric standards in use, there are 8 diameters defined but a total of 15 spanners are required! (i.e. 69% more spanners per diameters than the British system). Is this progress?"

I came up with these tables which show the 'irrational' whitworth /BSF hex sizes. I seem to remember that , certainly at one time, getting hexagonal bar in 'whitworth ' sizes was not an problem. We certainly had it in school early 1970's, and later on when I worked in engineering .

http://www.oldengine.org/members/diesel/Tables/WhitAF.htm

**LINK**

Edited By stevetee on 17/11/2016 19:47:28

Hexagonal bar in whitworth sizes is still available. Some sizes as mentioned are close to other nominal sizes 3/16 W 1/4 BSF are 0.440" A/F the next size up is 0.525" A/F other oddities follow. I think the original thinking was as a ratio of the shank diameter.

The glossary has attracted minimal contributions

Unlike the 'alternative' version proving our forum members have better knowledge of workshop esperanto than any other workshop language

Neil

.

Maybe your publishers were right [it's all on the internet]

... if only you can find it.

MichaelG.

This has perplexed me also. Found this explanation on the intenet at http://www.enginehistory.org/british_fasteners.shtml

The derivation of Whitworth wrench sizes is another obscure mystery. From a Jaguar enthusiasts' web site **LINK** "...the hex sizes were originally governed by the commercially available steel hex bar stock sizes, in the days before automated screw machines, when nuts and bolts were cut from hex bar stock."

My understanding was that Whitworth sized his hexagons so they could be produced reasonably easily from nomial fraction sized round bar stock. Probably by forging or rolling down as machines able to cut round down to size in production quantities were not common when he first promulgated the standards.

The large hexagons of the original Whithworth sizes appear to be derived from some intuitive internal stress assessment based on relative depth of thread and the amount of metal between the thread and the hexagon. Large heads being desirable anyway when bolting timber or not too accurately finished plates and beams together as was very common then.

We tend to forget how much and how rapidly basic stock material size and finish changed between Whitworths day and WW1 or thereabouts. From the viewpoint of the amateur and producers of modestly engineered componets series production WW1 standards are pretty much good enough. Just a lot more expensive (relatively) to achieve then. General state of the art in Whitworths time could be fairly, by todays standards, said to be "Gwad, that's rough, real rough.". The high priced, highly finished "artistic" products of clockmakers et al being totally atypical. We get a distorted view of the quality of things produced in the past because all the ordinary cheap stuff that most folks had to use fell apart and was binned long before the antique and similar buff were born.

clive

American fred?

I think you'll find that the "original" Whitworth had square nuts, and bolt heads, and these were forged by the black smith.

Ian S C

Very much like the old coach bolts that riddle my garden shed, they look forged.

Michael W