Here is an article I got from rec.motorcycles about Whitworth sizes
that I thought might be interesting.
Tim
jpg@europa.asd.contel.com (Janet Gunn) writes:
This is the email my father sent me about whitworth sizes -
I haven't been able to find any historical account of the origin of
Whitworth nut and bolt head sizes. In standardizing threads, Whitworth
mostly codified the accepted practice of the day (ca. 1850), so I imagine
he did the same with spanner sizes. However, we can perhaps deduce where
that accepted practice came from.
Data: T = nominal spanner size = actual thread size
S = actual spanner size
C4 = diameter of circle circumscribing a SQUARE of side S
C6 = diameter of circle circumscribing a HEXAGON of S across flats
C6C = calculated value of C6 (see below)
T S C4 C6 C6C
1/8 = 0.125 0.340 0.481 0.393 0.406
3/16 = 0.188 0.445 0.629 0.514 0.516
1/4 = 0.250 0.525 0.742 0.606 0.625
5/16 = 0.313 0.601 0.851 0.694 0.734
3/8 = 0.375 0.709 1.003 0.819 0.844
7/16 = 0.438 0.820 1.160 0.947 0.953
1/2 = 0.500 0.919 1.300 1.061 1.062
9/16 = 0.563 1.011 1.430 1.167 1.172
5/8 = 0.625 1.101 1.557 1.271 1.281
11/16 = 0.688 1.201 1.699 1.387 1.391
3/4 = 0.750 1.301 1.840 1.502 1.500
13/16 = 0.813 1.390 1.966 1.605 1.609
7/8 = 0.875 1.479 2.091 1.708 1.719
1 = 1.000 1.670 2.362 1.928 1.938
1 1/8 = 1.125 1.861 2.631 2.148 2.156
1 1/4 = 1.250 2.048 2.897 2.365 2.375
1 3/8 = 1.375 2.215 3.132 2.557 2.594
1 1/2 = 1.500 2.413 3.413 2.787 2.813
1 5/8 = 1.625 2.576 3.643 2.975 3.031
1 3/4 = 1.750 2.758 3.900 3.184 3.250
2 = 2.000 3.149 4.453 3.636 3.687
The values of C6 are a close, but not perfect, fit to the expression
C6C = (3/16) plus (1 3/4) times T
also shown above. (The actual values of the constants, from a least squares
fit with the APL domino function, are 0.188, 1.727.) The values of C4 are
not such a close fit to a simple expression; the nearest is
C4C = (1/4) plus 2 times T
but the least squares constants are 0.231, 2.115. So I think we can conclude
that, in the early 19th century, the usual instructions from the foreman
were 'Turn the bolt heads to about 1 3/4 times the thread size, plus 3/16",
and then mill them hexagonal.' I don't think the discrepancies between C6
and C6C are significant; measuring techniques were pretty inaccurate then.
At first I thought the dimensions of a square head would be the important
ones, since ancient nuts and bolts usually had this shape. But hexagons were
in widespread use by 1830, when Nasmyth had to invent a nut-milling fixture
to keep up with the demand for hexagonal nuts.
The confusion over what thread size goes with a given head size is due to
the fact that there are THREE related series of nuts and bolts:
Whitworth (old), spanner size corresponding to thread size;
Whitworth (utility), spanner size one size smaller than thread;
British Standard Fine, finer thread but same spanner size as
Whitworth (utility).
Cycle (C.E.I.) threads have a slightly different thread form from Whitworth
and B.S.F., and are mostly 26 threads per inch (small bolts) or 20 tpi
(larger bolts), with B.S.F. hex sizes.
I forget if I mentioned to you the etymology of 'spanner'. I doesn't come
from 'to span', in the sense of 'to reach across, as a bridge', but rather
from the sense 'to string a bow, to tension'. A spanner was the gadget with
which one wound the spring on a wheel-lock firearm, by turning a shaft,
usually with a squared end. Later, it was applied to a similar tool used
to tighten nuts and bolts.
I think you're right about the usage 'Team (teamname)', but this is only
speculation. The name of Hailwood's operation was 'Ecurie Sportive'. 'Ecurie'
means a stable, in the sense of a stud, or a string of racehorses.
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