> A full size Whitworth nut is  one and a half times the diameter + an
> 1/8 th. of an inch.

Now almost obsolete guideline: When designing any equipment using 
Whitworth threads nothing smaller than 3/8 thread diameter should be 
specified. This is because the large head size wrt thread size causes 
proportionally large spanners to be used and users' brains are 
programmed to apply "tightening torque" somewhat proportionate to head 
and tool size. A 1/4" thread will be happily shorn off by many people. 
This is much less so with systems that use much lower head/thread 
diameters.

This "rule" could be ignored at ones peril. Any amount of equipment 
did in fact use smaller diameters than 3/8".

Did I hear someone out there in the dark say BA, cycle thread, pipe 
threads, gas threads*  ... .


        Russell


* tapered ! :-)




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