Author Topic: Fasteners on douglas  (Read 5879 times)

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Offline MrWright

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Fasteners on douglas
« on: 01 Jan 2006 at 23:54 »
Hi all,
I hope that you all find as much entertainment in my questions as I do; my ignorance on Douglas’ is slowly eroding.  However, I must ask the rudimentary question: what is the dimensional standard for the fasteners?  Is it standard English fractional (1/2, ¼, 1/6 ect) or is it Wentworth (sp?).  I don’t even know enough about the Wentworth standard to define it (but I thought it was decimal based on 10ths and so-on).

The only reason I ask is that one out of every four fasteners doesn’t fit my standard wrenches.  I have every wrench (in multiples) down to the 32nd of an inch.

Thanks again, your American friend, lost in the world of Douglas.

PS the project is moving along fine.  I disassembled the rear suspension; the smell of old grease reminds me of restoring cars with my father.  Happy new year!

Offline trevorp

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Re: Fasteners on douglas
« Reply #1 on: 02 Jan 2006 at 04:06 »
a set of bsf or whitworth spanners and sockets is what u need
here in australia u can buy them cheaply at garage sales etc u may find it more difficult in the us
here is a link to thread sizes most bolts and nuts are bsf some are bsc they vary in thread pitch

Offline Doug

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Re: Fasteners on douglas
« Reply #2 on: 02 Jan 2006 at 04:48 »
The post war Douglases use British Standard Whitworth (BSW), introduced in 1841 for coarse pitch threads (later sometimes known as know as British Standard Coarse (BSC)) and British Standard Fine (BSF) introduced in 1908 for fine pitch threads. These are both 55º thread angle, rather than the 60º encountered on American and metric hardware. Screws under 1/4”, particularly in the electrical system, are British Association (BA) threads (proposed 1884, adopted 1903), these have a 47.5º thread profile with a full radius root and crest, and was based on the Swiss or Thury thread. There does not seem to be any apparent logic to the diameter and pitch choices on these threads! And if you think that sounds bad, it is much more standardized than some of the thread systems Douglas used before WW2. Now with that little bit of useless trivia is out of the way…

The dimensions across the flats of hexagonal BSW/BSC/BSF fasteners are also defined by a Whitworth standard. But the size stamped on the wrench has little to do with the actual dimension across the flats. Rather, it the size of the bolt or nut for which that wrench is suitable for. Or it use to be in olden days. At some point they started to use the next smaller size hex on fasteners, retaining the original size hex for ‘heavy duty’ fasteners and such, like on bridges, steam locomotives, and other heavy iron. So you have a situation where a 1/4” Whitworth wrench fits a 5/16” Whitworth nut, and a 5/16” Whitworth wrench fits a 3/8” Whitworth nut, and so on. Eventually after a few decades this was duly noted and the Whitworth hex standard was replaced by the British Standard (BS) wrench, just in time for metrification. The only difference between the Whitworth wrench and the BS wrench is the latter have been re-marked so they once again correlate to the fastener size. Some wrenches are marked in both “W” and “BS” sizes. How these peculiar hex dimensions were determined is quite simple, they are what Joseph Whitworth thought optimum!

Fastener size, wrench designation BS-W, and maximum dimension across the flats are as follows:


In the USA, Whitworth wrenches and socket sets are a bit of a specialty item. To think you could once buy them via the Sears store under the Craftsman tool brand name! Now you order them from the firms in the UK catering to the vintage British vehicle restoration, or DomiRacer/Accessory Mart in Cincinnati usually have some Whitworth tools, though supplies vary depending on what they have been able to get a good deal on.

These dimensions pertain only to external hexagonal head fasteners. Internal hexagonal drive cap head bolts (Allen bolts) use a fractional inch hex key, where the size of the key is the dimension of the hex. The most notable location of Allen bolts on the Postwar Douglas are the fasteners holding the transmission to the flywheel housing, and the cover of the positive stop foot change mechanism.

« Last Edit: 04 Jan 2006 at 02:49 by Doug »

Offline Chris

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Re: Fasteners on douglas
« Reply #3 on: 02 Jan 2006 at 09:11 »
Following a query by another member, I am in the final stages of completing an article defining most of the fasteners and screw threads used on 2.3/4hp Douglas models from 1910 to 1926. I hope to be able to post this within the next few days.

Offline trevorp

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