Read this in the August issue of Road and Track
[Tech Notes, by Dennis Simanaitis]
Whitworth Madness
Isn't it about time we salute Joseph Whitworth, British engineer and
author of the 1841 paper "A Uniform System of Screw Threads"?
Before this, nuts and bolts had to be retained in matched pairs, because
there was no hope of their matching otherwise. But the Whitworth System
brought a certain logic to it all. At least, for a while.
The System set standards for threads per inch, thread angle, pitch and
shape. There were two quirks, however: The threads were a bit course for
many applications, and Whitworth wrench designations were based on shank
size, not head or nut dimension. Each of these quirks came back to haunt
the Whitworth System.
By the early 1900s, the British Standard Fine (BSF) thread was adopted in
parallel use, especially for applications where vibration was a problem
with Whitworth hardware.
And in 1924 Whitworth bolt heads were all downsized, with the new British
Standard dimensions choosen so existing tools could still be used-but on
different bolts. [could this be the source of the wrench size confusion?]
For instance, an old bolt head with 3/8-in. shank was the same size as a
new bolt head with a 7/16 shank. So a 1924 Whitworth wrench would be
labeled 3/8W 7/16BS. With older tools you had recall just what size fit
which bolt. And whether the bolt was new or old. Or BSF. Or Metric.
Or American Standard.
There'll always be an England; I suspect because there'll always be some
poor beggar trying to figure out which wrench fits.
- Alan
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