Douglas Nut sizes

[Marcus]

There is a very useful listing on this site of the threads used on the early machines.

Is anyone able to provide the size of the nuts that Douglas used across the flats, were they standard Whitworth sized nuts, or like some of the threads, were they special to Douglas. If we can  find the information on the AF dimensions it would be very useful to add that information to the thread listing. Then when I need to make some new special nuts I might be able to source the correct size hex material.

Many Thanks

Marcus


Link added - Dave, 29Jan2022

[cardan]

Hi Marcus,

I'm sure it varies from model to model, but most hexes used by Douglas are the "obvious" BS sizes. So the bizarre threads like 17/64" (just over 1/4") use 1/4 BS hexagons. (In the very early days, Whitworth hexagons were the "next size up", thus a true "1/4 W" hex is the same as a "5/16 BS" hex - many spanners/wrenches are labelled to reflect this. So the hexes on 1/4 and 17/64 threads are those for 3/16 W - a bit over 7/16" AF.)

A few undersize hexes are used, usually for things like cylinder heads on ohv models where there needs to be clearance for a tube spanner. These are usually the next BS hex size down.

Plenty of drawings of the BS spec on the interweb, for example the second drawing here https://www.thomassmithfasteners.com/technical/

For threads smaller than 1/4" (3/16 W hex), hex sizes get messy. The next hex size down is usually 3/8" AF, rather than 1/8 W (which is what you'll find on the other end of your 3/16 W spanner).

Handlebar levers, electrical and carburettor hexes are often BA.

Gotta love a crazy thread, and hex!

Cheers

Leon

[Doug]

Douglas used a mix of spanner sizes, just to keep one on your toes! The DT spares list is one of the few I have seen where it actually mentions spanner sizes.

Part No.   Description                                                      Comments
6376        Box spanner, .7094 and .9191                        (Whitworth sizes)
    Yes, they used four decimal places in the spares list for a spanner stamped out of sheet metal!
6377        Box spanner, .4375 and .525                         (Fractional and Whitworth sizes)
2596-2    D.E. Closed spanner .9191 and 1.101 A/F       (Whitworth sizes)
6551        D.E. Closed spanner .525 and .4375 A/F        (Whitworth and Fractional sizes)
2594        Tappet spanner .525 and .375 A/F                 (Whitworth and Fractional sizes)
2597        Tappet spanner (S.E.) .4375 A/F                    (Fractional size)
and
8591        D.E. Spanner (Abington) Cyl. Head Nuts         (Size not given)
8330-1    Flat spanner (Head and Carburettor)              (Size not given)

Differentiating between 3/16 Whiworth (now 1/4 BS) at 0.445 inch Across Flats versus 7/16 fractional (0.438 inch) can be difficult with rusty and abused hardware. But the absence of a 0.445 spanner in the above list suggests that they preferred a fractional hexagonal bar stock for that particular size over Whitworth. However it does not say what the size of the wrench purchased in from Abington or the 8330-1 flat spanner is.

-Doug

[Marcus]

Thanks Leon and Doug,

That gives me a very good start. Having worked on British Vintage cars, most of my spanners are double marked, for example 1/4W or 5/16BSF, as BSF are one size smaller than BSW.

Kind Regards

Marcus

[cardan]

Differentiating between 3/16 Whiworth (now 1/4 BS) at 0.445 inch Across Flats versus 7/16 fractional (0.438 inch) can be difficult with rusty and abused hardware. But the absence of a 0.445 spanner in the above list suggests that they preferred a fractional hexagonal bar stock for that particular size over Whitworth.

So interesting!

It happens that there are people who have sorted original vintage Douglas nuts into zip-loc bags.

If we take 5/16-25 nuts - and therefore certainly Douglas - as an example, I can report:

1. There are 5/16-25 nuts that meet the BS standard: 0.525" across flats, and 0.250" thick. (Actually the thickness is slightly more than the standard , most falling into 0.255 +/- 0.005".) They are plain nuts, with no machined-in washer.

2. There are also 5/16-25 reduced-hexagon nuts. Looking at very original nuts, not rusted or ruined and maybe with original nickel plating, there are TWO sizes. Some (around 60% in my bag) are definitely BS hexagon (0.445 across flats), and are much longer than the Standard at mostly 0.345 +/- 0.005". The other 40% are definitely 0.4375 (7/16)" across flats and around 0.310 +/- 0.010" long. Both sets of nuts look like old, original, Douglas nuts!

I'm happy to agree with Doug's DT spanner references and say that some Douglas nuts were made from 7/16 bar stock, even if some others were Whitworth.

It's quite hard (but possible) these days to source imperial hex, and almost impossible to find BS hex. 7/16 sounds close enough.

Cheers

Leon

[Marcus]

Thanks Leon for posting those original nut details.

The situation in Australia regarding hex steel supply sounds the same as New Zealand, here we can get the fractional sizes like 7/16 easily, but not the BS sizes.

For some of the larger BS sizes, it is possible to use Metric which is readily available and pretty close in size;
3/8 BSW –  0.710"    18.034mm could use 18mm which is only 2 thou smaller
7/16 BSW – 0.820"   20.830mm could use 21mm, which is only 6 thou larger
And for 1.01 we can buy locally 1" which is only 10 thou smaller

However, if you want the BS sizes they are available in short lengths in the UK from a Company called "Metal Mania". You would need someone in the UK to forward them on to you in Australia.

Cheers

Marcus

[EW-Ron]

Don't forget that all (?) these nuts would have been nickel plated from new.
Quite a heavy generous coat too, it would seem.

This means a brand new or pristine spanner/wrench may have difficulty in fitting them ...