On Wed, 16 Aug 2000, Wiedemeyer wrote to Blair Engle:
> I've been following this thread on Whitworth tools and have finally
> gotten the nerve to ask just what is different between Whitworth sizes
> and standard American sizes? (ie) I notice that the sizes are given
> as 5/16, 3/8, etc.
American wrench sizes refer to the jaw openings. For example, a 1/2 inch
wrench fits a hex head 1/2 inch across the flats, which normally is a
5/16 inch diameter American bolt.
What we typically call "Whitworth" wrenches are marked two different
ways: Whitworth sizes and British Standard sizes. Both fit the same
bolts, and the sizes are in inches, but...
British Standard wrench sizes refer to the diameter of the bolt they fit.
For example, a 5/16 BS wrench fits a 5/16 BSF (British Standard Fine
thread) or 5/16 BSW (British Standard Whitworth coarse thread) bolt or
nut. Pretty straightforward.
Whitworth wrench sizes don't correspond to the bolt diameters of modern
British bolts, nor do they refer to the distance across the flats of the
hex head. The same 5/16 BSF or 5/16 BSW bolts require a 1/4 W wrench.
I've heard several versions of why this is so, none of them very
believable. Maybe one of our list members in the UK knows the real story.
Some American wrenches will fit some BS bolt heads, but not well. If
you're wotking on as T-Type you need wrenches in either British Standard
or Whitworth sizes. Either will do, but the BS sizes are easier to live
with because they correspond to the bolt diameter.
--
Chip Old 1948 M.G. TC TC6710 XPAG7430 NEMGTR #2271
Cub Hill, Maryland 1962 Triumph TR4 CT3154LO CT3479E
fold@bcpl.net
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