Pat wrote:
>
> NF = National Fine
> UNF = Universal National Fine
>
> Are they the same ????
AFAIK, Yes. NF is an earlier version of the same standard that became
(with some additions) Unified (not Universal) National Fine.
>
> 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 ....
I'm not familiar with UND, assume you meant UNF. There is possibly a
very small kernel of truth to this, but for fender bolts you will never
know the difference. The issue is not UNF vs NF, but rather what kind
of tap you use, and how the threads were originally formed. Rolled
threads are slightly stronger than cut threads. Also, most OEMs use
less than 100% threads (which are stronger), but most taps will cut to
nearly 100% (until they wear a little <g>).
>
> Where does "Whitworth" come into play ?
As commonly used, "Whitworth threads" covers several obsolete thread
standards that predate UNF, UNC, metric, etc. Some people claim only
BSW (British Standard Whitworth) are Whitworth, while most include BSF
(British Standard Fine), BC (British Cycle), BSP (British Standard
Pipe), BSPT (British Standard Pipe Tapered) and some also include BA
(British Association).
BSW was first proposed by Sir Joseph Whitworth in 1841, while BSF wasn't
introduced until around 1900. BA was adopted in 1903 to cover screws
smaller than 1/4 inch.
The most obvious thing about the Whitworth standards is that they base
the head size (and hence wrench size) on the bolt size. So, a 1/4"
Whitworth wrench fits a 1/4" BSW bolt, although the actual opening is
much larger than 1/4". To confuse the issue even more, BSF takes a
smaller wrench than BSW, so a 1/4" Whitworth wrench also fits a 5/16"
BSF bolt.
The Whitworth sizes also have a different thread angle (55 instead of
60, or 47.5 for BA). Most BSW sizes have the same thread pitch as UNC,
while BSF and BA are completely different. Some of the BA threads get
really wild, for instance #2 BA is 31-3/4 threads per inch.
Randall
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