JIS screw drivers

[Gone in 60]

I've had a set of JIS screwdrivers for years, going back to my old Hondas. These days, they're broken out every two years for the brake and clutch fluid flushes.
Now all I need is a set of Whitworth wrenches...

[Tev62]

GIN60, this will throw you, took me a while to get my head around this. On the MG TD, the engine and gearbox fasteners are known as "Nuffield Mad Metric." They feature old French Standard Metric threads paired with imperial Whitworth-sized hexagonal heads.

The MG XPAG engine and transmission were built using old French metric tooling from the Hotchkiss factory, which Morris/Nuffield had acquired. The threads are fine-pitch metric, not the standard metric you find in modern hardware. They had to keep the heads Whitworth to keep everyone happy.

The Story behind Whitworth is fascinating and his legacy still has a bearing in England with a Scholarship that still runs today.

In the 18th and early 19th centuries, complex machinery like steam engines and early automobiles required hundreds of fasteners. However, blacksmiths and mechanics created their own taps, dies, and thread profiles. If a bolt broke, you couldn't simply buy a replacement from a different factory; you had to have the exact machine shop that built the bolt forge a new one.

Sir Joseph Whitworth recognized the inefficiency of this system and began collecting samples of screws from workshops across England. Using these samples, he designed a system that struck a middle ground. His 1841 proposal to the Institution of Civil Engineers specified:

• A standardized thread angle of 55°.
  
• Defined thread pitches (threads per inch) for various diameters.
  
• Rounded roots and crests, which reduced stress risers and made the bolts significantly stronger.
  

Whitworth's system allowed manufacturers to buy compatible nuts and bolts from different suppliers, revolutionizing global mass production. The Royal Navy's Crimean War gunboats were one of the first major projects to utilize these mass-production techniques with standardized parts.

"You can only make as well as you can measure"
       - Sir Joseph Whitworth

   

"You can only make as well as you can measure"
       - Sir Joseph Whitworth "You can only make as well as you can measure"
       - Sir Joseph Whitworth

[Cormanus]

Fine looking CB1100, Tev!

[Gone in 60]

Very informative, Tev! I had just visited a good friend who restores early Phantoms. I was using his drill press and bench grinder to whip up a few box mounting plates for our company bikes. The tool chest nearest to the drill was labeled Whitworth, and his collection is necessarily impressive for his work. 

Plus, I get the question at my other job… “are these metric?”

[Nachodaddy]

Thanks, Tev. A bit of history that helps me understand a basic system I had always taken for granted. Getting a bit more educated after 85 years.