> I had someone tell me that the British used a different 'pitch' on the thread
> of a bolt. IOW, a SAE 7/16 x 24 (threads/inch) but, perhaps the closest
> British sized bolt is 7/16 x 25 tpi. Is this true
Well, not quite. SAE 7/16 only includes 14, 20 and 28 ... 7/16-24 is a
compression fitting thread.
And the nearest British threads would be 7/16 BSW, which happens to also be 14
tpi (although the thread form is different); or 7/16 BSF which is 18 tpi.
But it's quite true that there are a bunch of obsolete British thread standards
that are different than SAE standards. Not only is the pitch unique, so is the
thread angle, thread shape, and head size ! And there are quite a few of them :
British Standard Whitworth (BSW), British Standard Fine (BSF), British
Association (BA), British Standard Cycle (BSC or sometimes just BC), British
Standard Pipe Parallel (BSPP), etc.
Here's an identification chart I keep taped to the wall in the garage :
http://mdmetric.com/tech/tict.htm
Although, to be fair, there is quite a proliferation of obsolete American (SAE)
standards as well.
http://mdmetric.com/fastindx/t50u.pdf
FWIW, I've never found any BSW threads on a TR3. There are quite a few BA
threads, and maybe some BSF, and I never have identified the threads on the
studs that hold the gauges to the dash for certain ... they appear to be some
oddball metric thread. But no BSW.
Randall
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