> As has already been said, it's "Whitworth", but I'd be *really* 
> surprised if it had anything Metric on it.  I started work on cars 
> when I was about 10,
> and I didn't encounter anything Metric on a British car before those 
> made in about 1970.  Before that threads were UNF and UNC (unified 
> coarse and
> fine) and BSW (British Standard Whitworth).  UNx nuts and bolts used 
> "AF" (Across Flats) spanners, while BSW used Whitworth spanners, 
> which I
> believe were sized avvording to the diameter of the thread, so a 
> 1/2" AF open-ended spanner was 0.5" across its mouth, whereas a 
> 1/2"W spanner
> was much larger.
>
> Howard Winter
> St.Albans, England
>
>
A full size Whitworth nut is  one and a half times the diameter + an 
1/8 th. of an inch.

Cheers
Ian Stewart 

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