On 10/26/2010 3:22 AM, JOHN DUGGAN wrote:
> Argggghhhhh!
> The thread size is 1/4" BRITISH STANDARD WHITWORTH (BSW) Named after
> Joseph whitworth who invented this thread specification in 1841. Before ...
That's what the references say. Still, I have used North American 1/4"-20 UNC
thread nuts and bolts interchangeably with
tripod mounting bolts and sockets with perfectly good results for decades. I
suspect I've even used a UNC tap and/or die
to clean up damaged threads.
It seem to me that either the threads are so similar as to be interchangeable
in practical photographic use or the
standard has changed without documentation. Just recently, I ran a 3/8"-16 UNC
bolt through a Manfrotto QR plate
threaded hole to do a makeshift anti-rotation stop. It seems to fit perfectly,
screwing in smoothly and easily , but
with very little play. I just tried a 1/4-20 in the smaller hole in the same
plate - perfect fit, as far as I can tell.
The need for a thread standard for the Allies ( other than Russia) in WWII led
to introduction of UNC as the standard
for Britain before metric then took over. Perhaps tripod threads changed at
that time? The occupying forces would have
been using UNC throughout Western Europe for many years - another likely
influence on manufacturing standards. Or maybe
the transition of manufacturing from Europe to the Far East has led to a de
facto switch to the UNC standard?
Yes I know that the BSW spec is supposed to be stronger than UNC. Sure, British
threads and plugs are the best in the
world. (I first learned about the plugs in Help. ;-) ) Still, the thread specs
didn't end up being a major standard.
Screwy Moose
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