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[McMurdo]

Anyone out there that can explain the Whitworth sizing to me? I had read that the sizing on Whitworth spanners was to indicate the thread size and not the size of the hex-head so when I wanted to replace some fasteners with stainless I used the spanner size as a guide (1/4" spanner in this case). I also measured the hex flats (13 and a bit mm) and matched this to some tables that I found which indicated that this was 1/4" BSW.

Suitably assured, I ordered some fasteners from a couple of online stainless suppliers and sat back to await my delivery.

The parts arrived today and both the set-screws and the nuts were smaller than the fasteners on my bike. I queried this with both suppliers and both insisted that these were indeed 1/4" Whitworth and that the across the flats measure on the 1/4" hex should be 11.3mm (a 3/16 Whitworth spanner size)

So - what is the correct across the flat measure for a 1/4" Whitworth nut? And if my spanner / tables are correct at 13.335mm across then why do all the suppliers think they should send me the equivalent of 3/16?

Grrrrr!!

Stuart

[Daiwiskers]

Just had a hunt around all I can find are my whitworth sockets
The 1/4 socket is a lose fit on a 1/2" hex
Can't help with thread
Sorry Dai

[Daiwiskers]

Too late to edit
Just found
MARYLAND METRICS
THREAD DATA CHARTS
BRITISH THREAD -- COARSE PITCH -- BSW

Sorry can't do link with phone

It shows 1/4BSW thread having a diameter of 6.350mm

This is even more confusing

[Daiwiskers]

Found it
BSW spanner sizes are measured along one flat of the bolt or nut

BSW (British Standard Whitworth)
A coarse thread devised and standardised at Manchester in 1841
by British Engineer Sir Joseph Whitworth (1803 - 87). It is used in many types of engineering throughout the world,
although in Britain its use is now being superseded by the ISO metric system.

Angle of Thread = 55 Degrees

Sizes range from 1/16" to 2-1/2"

BSW Thread Data

In the 19th Century every British factory which needed to bolt something to something else devised their own fasteners to do it. Clearly, this caused all sorts of compatibility problems. So, along came Mr. Whitworth (I forget his first name right now) who invented a standardized system of coarse threads (with 55-degree thread angle and rounded roots and crests). This standardization was a Good Thing. Along with his threads came heads for the bolts that were based on the length along: the side of one flat, rather than across the flats. Hence, there is no simple fractional number for the length across the flats, which is why your imperial spanners don't fit. The fractional number on your spanners refers to the diameter of the bolt which is 1/4", 3/8" etc. not the distance across the flats (which ends up being various weird dimensions). Some years later the British decided they needed a finer pitch for some applications, so another thread series was introduced (same 55 degree angle). They also decided that the heads were too big for the bolts, so for most applications they switched to using the next size smaller heads. Because of this, and to add one more bit of confusion to life, one manufacturer will mark a particular spanner "3/8BS," while a different manufacturer will mark the same sized spanner "7/16W." They fit the same diameter bolt. The first thing any fledgling British car restorer learns is that his (or her) car has "Whitworth bolts." They think this is interesting, buy a set of "Whitworth spanners," discover these spanners fit their bolts, and believe they now know everything they need to know about British fasteners. Unfortunately, at this point they know only enough to make themselves dangerous. Instead, what they should have said to themselves is "Oh my God, what other weird and incomprehensible things have they done to the fasteners on my machine?" The answer to this question is:

British Standard Whitworth (BSW)

These are the original, 19th Century, coarse-threaded industrial bolts designed to hold locomotives together. Because of their coarse pitch, they are more prone to vibrating loose, so are little used on motorcars. Except for threading into aluminum (e.g. crankcase studs), where a coarse thread is less prone to stripping than a fine one. It turns out that, except for 1/2" (where the British use 12 threads per inch (tpi) and Americans use 13 tpi) the thread pitches for the rest are the same as for American Unified Coarse (UNC). However, the thread form is different; Whitworth = 55 degrees; UNC = 60 degrees. In spite of this, mismatched nuts and bolts mate nicely, so you're likely to find UNC bolts or studs where BSW should have been.


Diameter
Inches T P I Pitch
inches Core
Diameter Tapping Drill Size
1/16 60 0.0167 0.0411 Number Drill 56
(1.2 mm)
3/32 48 0.0208 0.0672 Number Drill 49
(1.85 mm)
1/8 40 0.025 0.093 Number Drill 39
(2.55 mm)
5/32 32 0.0313 0.1162 Number Drill 30
(3.2 mm)
3/16 24 0.0417 0.1341 Number Drill 26
(3.7 mm)
7/32 24 0.0417 0.1654 Number Drill 16
(4.5 mm)
1/4 20 0.05 0.186 Number Drill 9
(5.1 mm)
5/16 18 0.0556 0.2413 Letter Drill F
(6.5 mm)
3/8 16 0.0625 0.295 5/16 inch
(7.94 mm)
7/16 14 0.0714 0.3461 Letter Drill U
(9.3 mm)
1/2 12 0.0833 0.3932 Letter Drill Z
(10.5 mm)
9/16 12 0.0833 0.4557 12.1 mm
(0.4764 inch)
5/8 11 0.0909 0.5086 13.5 mm
(0.5315 inch)
11/16 11 0.0909 0.5711 15 mm
(0.5906 inch)
3/4 10 0.1 0.622 41/64 inch
(16.27 mm)
13/16 10 0.1 0.6845 18 mm
(0.7087 inch)
7/8 9 0.1111 0.7328 19.25 mm
(0.7579 inch)
15/16 9 0.1111 0.7953 20.75 mm
(0.8169 inc


Hope this cut and paste from british tools and fasteners helps

Cheers Dai

[McMurdo]

Nope - still in the dark

This is the same info I’d already read and if it is true then I’m still confused about the suppliers.

Why is it when I order a nut that fits my 1/4W spanner (ie 1/4 BSW) do they send a 1/4” BSW nut that fits my 3/16W spanner and has a 3/16 hole in it? If it was one supplier I’d put it down to stupidity but they’re all doing the same!

Stuart

[Daiwiskers]

I think the way to go is to measure the fixing you have then go to the charts and order from there
The spanner size doesn't seem to matter as long as it fits
Fun little project Dai

[Daiwiskers]

Too late to edit again

It seems the spanner size bears no relation to the thread size just to the length of one side of the hex of the fasteners
No idea why Dai

I do feel for you both asbo30 and my Harley have a mixture of AF Whitworth and metric

[Daiwiskers]

Stolen from Wikipedia

To simplify matters, the term hexagon is used in this section to denote either bolt head or nut.

Whitworth and BSF spanner markings refer to the bolt diameter, rather than the distance across the flats of the hexagon (A/F) as in other standards. Confusion can arise because each Whitworth hexagon was originally one size larger than that of the corresponding BSF fastener. This leads to instances where for example, a spanner marked ​7⁄16 BSF is the same size as one marked ​3⁄8 W. In both cases the spanner jaw width of 0.710 in, the width across the hexagon flat, is the same.

Certain branches of industry used Whitworth fasteners with a smaller hexagon (identical to BSF of the same bolt diameter) under the designation "AutoWhit" or Auto-Whit[citation needed] [6] and this series was formalised by the British Engineering Standards Association in 1929 as standard No. 193, with the 'original' series being No. 190 and the BSF series No. 191.[7]

During World War II the smaller size hexagon was adopted more widely to save metal[8] and this usage persisted thereafter. Thus it is today common to encounter a Whitworth hexagon which does not fit the nominally correct spanner and following the previous example, a more modern spanner may be marked ​7⁄16 BS to indicate that they have a jaw size of 0.710 in and designed to take either the (later) ​7⁄16 BSW or ​7⁄16 BSF hexagon.[9][10][11]

Whitworth fasteners with the larger hexagons to BS 190 are now often colloquially referred to as 'pre-war' size, even though that is not strictly correct.

Cut and paste from the Wikipedia Whitworth page the above is just the spanner part

So it looks like the spanners are marked with the earlier sizes and the fixings are sold with the later smaller hex sizes

[McMurdo]

Ah - now it's totally clear ….

So a 1/4" BSW spanner has a jaw size of 13.25mm but a 1/4" BSW nut has a width of 11.303mm and a 3/16" BSW spanner is also 11.303mm. Totally obvious now you've explained it

Cheers Dai

Stuart

[Wheaters]

I love metric....