Patrick :
I don't have my reference works handy, but here goes :
Back at the dawn of the Industrial age, there was no standard for
threads, no such thing as a standard bolt, wrench, etc. This made
spares, etc. an absolute nightmare and the need for a standard was
obvious. Joseph Whitworth, an engineer, proposed a system of standard
'optimum' threads that were adopted by the British government as
"British Standard Whitworth" or BSW. (And Sir Whitworth was knighted for
his efforts.) One of the more unusual features of his system is that
bolt heads (ie wrench sizes) are proportional to the bolt diameter and
are so classified by the bolt size. Thus, a 1/4" Whitworth wrench fits
a 1/4" bolt or nut, even though the actual head size is much larger.
The Whitworth picture is further complicated by the later development of
several similar systems for various reasons, the most confusing of which
is BSF (British Standard Fine). BSF fasteners have smaller heads than
BSW, but to enable use of the same wrench set, they made each BSF
fastener take the wrench from the next smaller BSW fastener. Thus, a
5/16" BSF takes the same wrench as a 1/4" BSW.
A perfectly good system, but unfortunately not one adopted by most other
countries, who all wanted their own standards. Thus we have SAE in the
US, and various flavors of metric in other countries. Some 90 years
ago, I believe the UK government mandated a change to SAE threads (which
were to become an international standard). Unfortunately, most other
countries refused to follow suit (being unwilling to ride on the US's
coattails, as it were). Relatively recently (as such things go), a
bunch of people got together and once again agreed to standardize on a
single world system, ISO metric. Whether it will happen remains to be
seen <g>
Anyway, it took a long time for all the British manufacturers to make
the switch, and the mish-mash of different threads found on our LBCs
reflects that. A TR2/3 has only a smattering of Whitworth threads
(mostly on the carbs and electrical equipment), with a couple of odd
metrics thrown in for good measure. TR6s have almost no Whitworth
threads (maybe none), and a few more metrics, while I understand TR7/8
are roughly 50% metric. (In all cases, the balance is SAE.)
FWIW, the US government agreed to make metric the US standard back in
the 1960s. US cars are the only place I've seen the change, and IMO
it's mostly because they no longer build them in the US.
Randall
"Bowen, Patrick" wrote:
>
> Could someone explain Whitworth sockets to me. How are they measured, how
> are they different. What were they used on. The only reference I ever see
> is in regards to british motorcycles.
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