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Chinese Threads?

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Vic05/08/2020 15:14:27
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I’ve been looking at a few bits for doing some macro work with my camera. Some of them are so cheap it’s not worth making them yourself. The only problem is that some parts don’t appear to use the correct threads. As many know the standard tripod thread is 1/4” BSW and many parts are designed around this. Some parts though just say 1/4” X 20 thread so could be anything, others actually state 1/4” X 20 UNC which obviously isn’t correct. I wonder if the Chinese actually know the difference?

JasonB05/08/2020 15:19:11
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I think we have discussed this before and UNC seems to be the norm now. I'm sure Michael knows where the thread about threads is.

Maybe the Chinese are more on the ball than you by not using old Whitworth!

"

Screw thread[edit]

Per ISO 1222:2010,[1] the current tripod screw thread standard for attaching the camera calls for a 1/4-20 UNC[2] or 3/8-16 UNC thread.[3] Most consumer cameras are fitted with 1/4-20 UNC threads. Larger, professional cameras and lenses may be fitted with 3/8-16 UNC threads, plus a removable 1/4-20 UNC adapter, allowing them to be mounted on a tripod using either standard.

Historically, The Royal Photographic Society recommended the thread standard for attaching older cameras to tripods was 3/16-24 BSW (3/16 inch nominal diameter, 24 threads per inch), or 1/4-20 BSW[4] for smaller cameras and 3/8-16 BSW[5] for larger cameras and pan/tilt heads. In this application, the BSW and UNC thread profiles are similar enough that one can mount a modern camera on a legacy tripod and vice versa. The UNC threads are a 60-degree angle and flattened, whereas the BSW are a 55-degree angle and rounded crest. However, at least one English manufacturer uses No.1 B.A. (British Association) for its tripod mount thread.

Edited By JasonB on 05/08/2020 15:29:20

Emgee05/08/2020 15:24:17
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Vic

Probably using 1/4"20 UNC as that allows both Whit and UNC to mate, but obviously a bit of a free fit with Whit, doing it the other way would not suit both.

Emgee

Vic05/08/2020 15:57:10
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I’m pretty sure all my old stuff is 1/4” BSW. I wonder when it was changed and why? The Europeans would obviously have been upset to use a “British thread” but let’s be honest there’s no love lost on the Americans either! I’m glad they didn’t have the sphericals to go M6 coarse as having cut some 1/4” Whitworth a while back it occurred to me at the time that it’s a much nicer thread to cut. It also seems less susceptible to cross threading. I should add that most of my thread cutting is normally in metric as the fasteners are easier to source. I only resort to imperial threads to fit American and Chinese stuff!

Tim Stevens05/08/2020 16:56:53
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As most of the camera bits are aluminium or plastic I suggest it makes very little real difference whether the form is Whit or Unified. Certainly not after the first week or so of changing bits around.

Cheers, Tim

JasonB05/08/2020 17:07:37
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You could probably even get away with a metric form cutter at 20tpi or 1.25mm on a 6.35mm blank

Tony Pratt 105/08/2020 17:08:40
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Posted by Tim Stevens on 05/08/2020 16:56:53:

As most of the camera bits are aluminium or plastic I suggest it makes very little real difference whether the form is Whit or Unified. Certainly not after the first week or so of changing bits around.

Cheers, Tim

Used to do it all the time in industry.

Tony

Hopper05/08/2020 23:14:56
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Commercially made UNC and BSW in general will fit together if diameter and tpi are the same. Commercial threads are not made to the precision full form standards beloved of model engineers but are made slack to fit any mating component from any other manufacturer worldwide.

Barrie Lever05/08/2020 23:28:46
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Hooper

The exception is 1/2", one is 13 tpi and the other 12 tpi

B.

Michael Gilligan05/08/2020 23:37:58
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Posted by JasonB on 05/08/2020 15:19:11:

I think we have discussed this before and UNC seems to be the norm now. I'm sure Michael knows where the thread about threads is.

[…]

.

Sorry, Jason ... I wasn’t around today

But you’ve done me proud !

MichaelG.

.

P.S. ___ This is worth reading [even if I have to admit to making an error or two therein]
https://www.model-engineer.co.uk/forums/postings.asp?th=91355&p=1

... We got there in the end !

Edited By Michael Gilligan on 05/08/2020 23:45:04

SillyOldDuffer06/08/2020 14:04:37
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Posted by Vic on 05/08/2020 15:57:10:

I’m pretty sure all my old stuff is 1/4” BSW. I wonder when it was changed and why? ...

Though widely used I don't believe 1/4" BSW was ever the world standard. The Royal Photographic Societies recommendations brought order out chaos, but even in the UK 1/4" BSW wasn't universal. Plenty more alternatives around the world.

Switching tripod threads to the Unified Thread System must be blamed on the Western Allies suffering considerable supply inconveniences during WW2 due to equipment incompatibilities. As a result Whitworth threads were deprecated at the end of 1949. Back-compatibility required Whitworth to carry on, but his thread system fades away year by year. Unlike his historical significance, which remains rock solid!

IS1222:1973 is the earliest International Standard covering photographic threads I could find. So 1/4" BSW has been off the agenda for 47 years. The Chinese are only as confused as the rest of us!

Although Metric Threads now dominate world engineering, someone on that side of the fence must have decided IS1222 was good enough. Best left alone like BSP.

Dave

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