Well, I note from the CR pages, that Williams was based in Foundry Lane, Smethwick. I was born just half a mile from their factory, and did my Engineering apprenticeship with W & T Avery's, which is even closer!! Proximity ought itself to make me an expert on their threads used, but it doesn't ;-( My best guess, going from the times and the culture, is that Williams has to have some weirdass british threading going on there.
As a small aside, Avery's has a building on-site still which is now used for the assembly of large weighbridges. I am talking about things big enough to drive a laden Loco across and get the weight. Maybe that's not such a big deal now, in the age of strain gauges simplifying things, but back in my day these weighbridges were built using beams and knife-edge pivots. Imagine the strains involved (Very on-topic)!! It was in this building, then a Foundry, that Mathew Bolton who developed the first steam engines, and thus helped spawn the Industrial Revolution, had an underground tunnel built from the Foundry to his house on the hill. he was a wealthy man, and wanted safe passage. If only he had developed the bicycle instead, he would still have been ahead of his time, and ahead of the people trying to waylay him.
Neill Currie..........who's first bike with a mere 2 wheels was a dropped bar BSA 3 speed, bought in a shop in the shadows of the Aston Villa Football Club stadium (Now, does anyone know of that shop, back in 1960?) Hillsborough, Nh, USA.
My blog, bike related, I think, is at http://blogericious.blogspot.com/
The Mountain Goat bicycle website is located here:
http://www.geocities.com/
AB-77(splined-cotterless)crank
>
> Joe Bender-Zanoni pointed out
>> I think the answer is 8mm X 1.25 which is a standard metric
>> coarse thread! Even if 5/16X20 is right, the metric size is
>> is so close it should work anyway.
>
> Yay! Thanks Joe. I just checked with some bolts I had - 8 x 1.25 is a
> very common thread - on bicycles it is found on many Japanese handlebar
> stems, like SR and Nitto. First one I tried didn't thread in, then I
> noticed the first thread was banged up. Second one also no-go - also a
> bad thread (what's the chances of that? At my house, a sure thing
> apparently). Unthreaded the third bolt from inside a nut, so it was a
> known-good thread, and it fit perfectly! Well actually a bit BETTER
> than the original-equipment bolt, but I can live with that! ;)
>
> 8mm is a TINY bit bigger than 5/16" (two and a half thousandths of an
> inch bigger), enough to take out some of the wiggle that the Williams
> bolt had. And 1.25 mm thread pitch works out to 20.3 TPI - close enough
> to 20 TPI that the bolt doesn't begin to bind noticeably over the
> half-inch or so length of engagement, despite being slightly oversized.
>
> Since everything I'm looking at and measuring is grimy, and made to
> fairly loose tolerances, there's a chance the Williams was actually made
> to fit 8 x 1.25, not 5/16" 20 TPI as I said earlier. Given how close
> they are, we may never know unless some Williams factory documents
> surface.