Bob,
Absolutely, positively, no doubt in my mind! UNF = SAE Fine and UNC = SAE
Coarse. It was set up this way when the British transitioned away from the
Whitworth Standard. Now, I initially was going to write that the two were
virtually identical because there are some minor differences, but I thought
that this would confuse some people with minutia. The differences are too
minor and they are interchangeable.
If yours don't fit then something is amiss and you'll need to find out what
the problem could be. Don't necessarily go by the Moss Catalog. First, get
a proper thread gauge and check for yourself. Whitworth thread gauges are
not that hard to come by and I have several. Check against US Thread gauge
to be certain.
First make certain the threads are perfectly clean, and if possible I clean
them on a wire wheel.
If the threads are damaged in any way this could be your problem. I've had
stretched fasteners with this problem where they will start to thread in and
then bind up. When a used a die I would start to cut threads. "British
Butter Bolts" is an accurate description and any stretch will cause what you
describe. I've also had bolts where the threads became damaged and would
bind up.
Next, don't use cheap taps and dies. My Whitworth stuff is high quality
German made of HSS, and the same goes for my UNF & UNC taps and dies,
quality made from the UK. The stuff they sell at local US hardware stores
is not always up to par in my opinion (feel free to interpret this as CRAP.)
A lot of my information has come from my 16th Edition, 1959 Machinery's
Handbook and many articles that I have research over the years. Plus 35
years of mucking around with Austin Healeys.
Oh, and FWIW there are several more obscure Whitworth thread forms which
include...
British Standard Screw Threads (Taper) for Copper Pipes.
British Standard Electrical Conduit (BSEC)
Model Engineers (ME)**
And there's more, but I won't go into them since they'll really obscure the
issue, but just remember, to be Whitworth they MUST have a 55 degree thread
angle.
Cheers,
Curt
On Mon, Nov 30, 2009 at 9:01 AM, Bob Spidell <bspidell@comcast.net> wrote:
> re: "*Unified Fine (UNF)* - Identical to American SAE Fine and
> *Interchangeable*. The angle of the threads is 60 degrees."
>
> Are you sure about this one? For instance, the threads on the large U-bolt
> that fastens the axle to rear springs is noted as 'UNF' in, for instance,
> the Moss catalog. I believe they are either 5/16" or 3/8." Anyway, we
> tried to run SAE fine nuts on them--they'll go about 3/4" inch just fine,
> then jam. A thread chaser will go 3/4", then cut, then go 3/4", then cut,
> etc.
>
> Same story with some of the nuts and bolts on the shock hardware.
>
> bs
>
> --------------------------------
>
> Bob Spidell - San Jose, CA
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