The Wiki entry on the subject of tripod threads says:
---------------------------------------------------------------
The historic standard threading for the bolt that attaches the camera to
the tripod is 1/4"-20tpi (threads per inch) British Standard Whitworth
(Whitworth or BSW) for smaller cameras or 3/8"-16tpi BSW for larger
cameras and pan/tilt heads. Bolts using 1/4"-20 UNC and 3/8"-16 UNC
screw threads are generally close enough to work when BSW bolts are
unavailable. Note: A BSW bolt in a UNC nut has play, but a UNC bolt in a
BSW nut will jam.
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But I have used many UNC bolts in tripod threaded "nuts" and they've
always fitted quite well. Never had a jam.
Chuck Norcutt
On 10/26/2010 3:19 PM, Moose wrote:
> 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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