Pat wrote:
>
> Okay all ...
>
> The debate has started (Sorry, I asked the original question..)
>
> NF = National Fine
> UNF = Universal National Fine
Actually, UNF is short for Unified National Fine. Today, the two terms
are probably used interchangeably, but sixty years ago or so, a lot of
fastener manufacturers had their own thread profile standards. These
were standardized during WWII by various manufacturing councils (such as
the Joint Industry Council, from whence comes the term in hydraulics for
a particular flare fitting, JIC, which always indicates a 37 deg.
flare). In earlier times, even though the pitch and bore size might be
the same, the pitch angle or tooth shape varied by manufacturer, and
therefore, so did the degree of thread engagement.
> Are they the same ????
For practical purposes today, yes, I think so.
> I'm told that if I tap out a 1/4 x 28 UND fender bolt nut and use a NF bolt
> that the threads will have been weakened ....
That's probably not because of the hardware used, but rather by using a
tap to clean out the cage nut. Any time this is done, some degree of
thread engagement is lost. That said, wing-to-body attachments are not
critically stressed areas, and if it is necessary to run a tap through
the cage nut to clean the threads, it's quite safe to use the existing
hardware in that area. The bolt may fit a bit more loosely, but applying
a little of the light-holding Loctite to the threads will prevent them
from loosening later, but will still enable them to be removed.
> Where does "Whitworth" come into play ?
Whitworth is an old, possibly defunct British standard (Brits on the
list might be able to say if it is still used anywhere in modern
manufacturing). If I recall (haven't worked on anything with Whitworth
in almost thirty years), the head sizes were based on a different
standard, so a special set of tools was required. The other major
difference with Whitworth hardware was the tooth profile. Whitworth had
rounded roots and crests, while all unified hardware today has flat
roots and crests (easier to make).
Cheers.
--
Michael D. Porter
Roswell, NM
[mailto: mporter@zianet.com]
`70 GT6+ (being refurbished, slowly)
`71 GT6 Mk. III (organ donor)
`72 GT6 Mk. III (daily driver)
`64 TR4 (awaiting intensive care)
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