Ron,
Here is a quote from:
<http://www.homemetalshopclub.org/news/feb03/feb03.html>
"Tom Moore presented a program on threaded fasteners followed by Joe
Scott's comments on screws used in gunsmithing: The difference between
a screw and a bolt is that a bolt has a nut on it and a screw does not.
They can be identical except for this feature. Threads fall into three
categories- assembly, fasteners and transitional. Assembly threads are
what are in cameras, for instance. Fasteners are usually a standard
thread and can fit many locations. Transitional have some of both
features. Threads were first standardized in Europe by the English
engineer Whitworth by averaging all the different threads used by
English manufacturers. They have a 55 deg. angle thread. The French, not
wanting to use English threads, devised the metric system. In America,
Mr. Sellers set up the first standards with 60 deg angle threads. Some
of his numbered threads were the same as used by American clock makers.
A fine thread was used for thin materials. These threads became the
American National Std. In 1920s the Society of Automotive Engineers set
standards for class of fit and dropped some of the in-between numbered
threads. This enhanced mass production of automobiles. They also set up
an extra fine pitch, so that there were three pitches; fine (SAE), US
Standard( coarse) and EF (extrafine). There was also a standardization
effort by the US military to make threads common to their needs.
Sometimes you see reference to AN threads, they are Army-Navy Standards
and are no longer used. The 1903 Springfield rifle was based on the
German Mauser patent and its threads are the nearest inch conversion
from metric, such as 1/4-25. In WWll, the odd threads were completely
dropped and Unified threads were established, such as UNC, UNF, UNEF
with class of fit specified. Metric threads have been standardized also.
We now use ISO threads for many uses. A general note: English threads
use round roots and crests and are different than ours. The English and
Japanese still use 55 deg. angles for their pipe threads. It is
extremely hard to get our 60 deg. pipe thread to seal against 55 deg.
Many of the cheap die sets have pipe dies and taps with 55 deg. Check to
see if it says NPT (60 deg) before using. If it doesn't say anything, it
is probably 55 deg."
The Brits did NOT standardize for WW II, and my 1952 MG-TD, and '54 Jag
120M were still Whitworth. I don't believe that automobile production
changed to conform to US standards until the 60's. As a matter of fact,
the Tigers and Alpines still had at least one strange bolt in the seat
assembly.
Supporting the 1960's estimate, as well as providing some interesting
other fastener issues of the Brits, can be found on:
<http://www.moreg.org.au/whitworth.htm>
Cheers, and use a pipe wrench. ;-)
Steve
___
Steve Laifman
Editor - TigersUnited.com
Ron Fraser wrote:
>Buck
> UNF is the Unified bolt series that the US and Great Britain put
>together during WW II so they would be compatible. There is a slight angle
>of the thread difference between them. The British Whitworth thread
>series is the odd ball to us in the states.
> The stock 1/2 UNF bolt has 20 threads per inch and the length of the
>threaded part is 1 5/8". Any replacement bolt has to have the same thread
>number and thread length equal to or more than the original bolt.
>
> I don't recall anyone damaging the lower threads but it is very
>possible. I would more suspect damage at the upper threads because the top
>of the threaded tube is exposed to the elements and generally has rust
>there.
>
>Ron Fraser
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