Dave Plowman (News) wrote:
In article ,
Andy Wade wrote:
Don't think that's so at all. There are very few sizes where AC will fit
Whitworth - and none I know of where AF will fit BSF. They were
essentially new threads to a common standard.

AC and AF? Do you mean American Coarse and Fine? I've not heard of
those designations before. Pre-WW2 American threads were NC and NF
(National Coarse/Fine) [1].

They tend to be known as American coarse and fine here - or at least in my
circles. ;-)

The unification which gave us UNC and UNF
[2] was, AIUI, not so much about making US parts interchangeable with
our BSW and BSF as about having a common standard adopted on both sides
of the pond.

Correct. But those unified threads owed far more to NF and NC than BSW or
BSF.

The Yanks would use UNC/UNF instead of NC/NF and we would
use UNC/UNF instead of BSW/BSF. This was only partially successful
because Whit-form parts remained widely available and used in the UK -
although the automotive industry did eventually switch to Unified.

And NC and NF are still common in the US. Sadly unified not so in the UK
as it was a far better system for general use than metric, IMHO.

Rubbish. Life wouldn't be the same without M3, 6BA, 1/8" whitworth, 1/8"
UNC and UNF..