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Are you confusing yourself perhaps? The 2BA is close to a 5mm coarse but the 0BA is almost identical to a 6mm coarse other than the thread angle. They both have a 6mm o/d and 1mm pitch.
Reply to
Dave Baker
Thanks, that did it - it's probably 2BA, as the pitch is a little bit more than M5, 31.36 tpi vs 31.8.
Sheeesh! There's a lot of threads about. Found this:
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the comments by secondjeremy and Hybrid_From_Hell seem particularly apt.
-- Peter Fairbrother
"By and large at the end of the 1930's the British motor industry was using the BSF (British Standard Fine) thread standard for its fixings. Other parts of industry used BSW (British Standard Whitworth) threads but the head sizes were similar even if they had different size designations and the BSW head sizes had been re-calibrated.
One of the exceptions was Morris engines which used what was essentially a metric thread with BSF head. This is another story.
BSF threads are quite fine and so considered not the best for fixings in soft alloy castings - so its common to find a BSW thread used there.
All was happy until about 1948 when it was universally decided that the UK should standardise on the American Unified threads (UNFine and UNCoarse) The more common is the UNF thread which is finer than BSF and has smaller heads with the head being measured across the flats (AF)
In 1948 the Land Rover hatched and being the latest technology it used BSF threads for most applications.
In the late 50's or early 60's it was decided that the UK should now standardise on the Metric thread system - so the series 2 Land Rover was introduced with Unified (UNF) threads. In fact they seem only to have been applied to the new bits - so you find plenty of BSF threads which were left there to remind mechanics of their youth when they worked with BSF all the time unless they were dealing with a Morris."
Reply to
Peter Fairbrother
John BA has its roots in metric dimensions
eg the pitch = 0.9mm^BA number
4BA pitch =0.6561mm 2BA pitch =0.81mm
Bob
Reply to
Bob Minchin
To add a little more confusion, don't forget the thread angles. 60deg for metric and American threads, 55deg for Imperial (BSW and BSF) and 47.5deg for BA. So metric and BA aren't really compatible!
John
Reply to
John
To add a little more confusion, don't forget the thread angles. 60deg for metric and American threads, 55deg for Imperial (BSW and BSF) and 47.5deg for BA. So metric and BA aren't really compatible!
John
And then there's the question of root and crest rounding (Whit / BSF) or truncation (American Sellars thread)...
AWEM
Reply to
Andrew Mawson

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