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:
"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
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.
"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