[ARC5] Parts needed for ARC-5/274-N - splines...

[Mike Hanz]

On 5/26/2014 5:51 PM, AKLDGUY . wrote:
>> ...since the thread is actually 1/2-27.
> Any chance that the thread is British/Euro?

Excellent question, Neil.  Since I first encountered the thread on a 
Bendix product, and they did a land office business with the 
Commonwealth before and during the war, I spent quite a bit of time 
going through my Machinery's Handbook for 1945, hoping it might be for a 
British or common metric thread.  At least then I could possibly find a 
friend with a British car who might have the tap. It was at the end of 
going through hundreds of thread forms that I happened on the gas pipe 
reference.  These are not tapered pipe threads - they're straight.  If 
the mating threads are of dissimilar metal and you use an anti-seize, 
then you can get away with a bit of mismatch.  Aluminum on 
aluminum...well, I can almost guarantee something will break trying to 
take it off at some future date.

> Many decades ago I scouted around the hardware stores and vehicle parts
> stores here in Auckland and found a pipe fitting that could be screwed on
> by hand, so the threads were either identical or very close.
>
> The fitting was of brass and of the type that connects fuel line to
> carburettor in vehicles. I can't remember whether I had to drill out the
> hole or not, but do remember that the shaft was eventually a snug fit
> inside it.

That happens a lot, and with tapered pipe threads you have a better 
chance - they typically have coarser threads and you can usually get it 
to seal up at some point.  Sadly, with fine straight threads, it is luck 
of the draw.  I finally lucked into a sale at MSC, a large machinist 
supply house here in the U.S., who put all their "special" tap threads 
on sale.  I went a little overboard, but at least they were halfway 
reasonable rather than eye-popping.  I mean, one can always use another 
tool or two, right? :-)

     73,
  - Mike