On or around Fri, 27 Jan 2006 14:25:56 GMT, SpamTrapSeeSig
<
[email protected]> enlightened us thusly:
>In article <[email protected]>, Badger
><[email protected]> writes
>
>>The bolts are 1/4 UNC thread, BTW, even the later ones with a bi-hex
>>8mm head!
>
>The mind fair boggles when you remember the "U" stands for "unified".
>
>I have visions of the fledgling US engineering industry with 20
>different not-quite-matching variants of the same threads. Must Google
>for the real history of these some time. Incidentally, my dad and
>various other engineers have always said that the old non-metric thread
>forms were better for different applications than the metric
>'compromises' (his word). I'm not well versed enough to know, but I can
>see some sense in it - Whitworth, for example being designed to undo
>even when badly abused or gunged up, or so I was told.
The whitworth thread was "designed" by Whitworth who took and average of a
selection of threads he had to hand at the time. Later the BS lot got a
hold of it and at some point people decided that Whitworth was a rather
coarse thread, and so you get BSF as well. When whitworth derived his
standard, bolts were typically mostly rather coarse and crude, I suspect -
witness the fact that most modern whitworth bolts have nuts and heads the
next size down - the 1/4" whitworth spanner (about 13mm) fits bolts with a
5/16" diameter, and you hardly ever see 1/4" bolts with that size head.
Meanwhile, other people came up with other standards, such as the SAE
(Society of Automotive Engineers), which had different thread forms and
different head sizes - measuring the head in inches across flats (which
makes more sense, really). At some point, someone decided that it would be
nice if all the inch-size threads fitted a common standard, and you got UNC
and UNF (Unified Coarse and Fine), although plenty of threads continued to
be used such as BS Cycle which used, IIRC, a whitworth thread form but with
a standard pitch of 26 TPI irrespective of size) and BA (British Association
- of what I forget) which are a law unto themselves but were for a long time
used on electrical stuff - BA threads have a very narrow thread form, IIRC
37.5°.
The people who were doing metric threads had less of a checkered history I
think, probably mainly 'cos they started later and had the prior example of
the muddle of imperial standards to steer clear of...
somewhere I have a damned great document which lists almost every thread
there is sorted by size.
--
Austin Shackles.
www.ddol-las.net my opinions are just that
"My centre is giving way, my right is in retreat; situation excellent.
I shall attack. - Marshal Foch (1851 - 1929)
