1/2" x 18 TPI thread?

Got to do a small repair for an old lady that lives up the road, which involves making a new ferrule to fit into the arm of a magnifying
light. Current part is a zinc casting where the internal thread has stripped off.
The weird thing is that the bolt that goes into this is 0.500" x 18 TPI thread (and I did measure correctly..) - seems a bit of an odd size to me as I can't find it on any of my threading charts. Anyone know what it is?
Screwcutting is not a problem (workshop back in action next week thank goodness) but I'm just curious as to the origin of this thread.
Peter
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which
thank
I believe 1/4 NPT is about 1/2" o/d x 18 tpi
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On Sun, 18 Mar 2007 13:15:59 -0000, "Andrew Mawson"
wrote:

1/4" ANP is 0.540 x 18
Conduit is 1/2" x 18 -- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:- http://www.homeworkshop.org.uk /
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On Sun, 18 Mar 2007 13:37:46 GMT, John Stevenson

Thanks John, thats almost certainly what it is then. I've now found a table for these threads on the oldengine.org site which confirms the rest of the detail matches up.
The outside thread on the ferrule screws into a tube, and I assume that this is also a conduit thread , although at 15/16" x 16 TPI it is a little bit undersizeon diameter, perhaps confirmed by the loose-ish fit in the tube. Thanks again
Peter
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Is it whitworth form as there is a 1/2" x 18 TPI anerican UNS thread
0.490 over major Dia
Steve Larne
-- Steve Larne ----------------------------------------------------------------------- Steve Larner's Profile: http://www.rcgroups.com/forums/member.php?u 733 View this thread: http://www.rcgroups.com/forums/showthread.php?te857
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On Sun, 18 Mar 2007 12:26:49 -0500, Steve Larner

Hi Steve, it's definitely a 55 deg form, perfect fit on the thread gauge, and just a shade over 0.500"but thanks for the info anyway.
UNS is the 'special' form over there isn't it -any particular purpose it gets used for?
Peter
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wrote:

UNS is a catch all for threads that are no longer in general use, and special purpose threads. Some are listed as NF, and NS. One example is 1/4 - 40. I have two taps in this size, one is marked NS and the other NF. Uses? Firearms, electrical fittings, model spark plugs, and older equipment. I am aware that 1/4 - 40 is standard for model spark plugs, and percussion nipples. I have yet to check to see if any of the NEF (National Extra Fine) threads are also NS.
Steve R.
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Steve R. wrote:

I have not seen a model spark plug in 1/4-40, but rather a lot in 1/4-32. Same as the current standard for glow plugs on model airplane (etc.) engines.
Cheers Trevor Jones
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wrote:

OOPS I meant 1/4 - 32. Gotta quit posting this stuff in my sleep!
Steve.
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Steve R. wrote:

It's allright! I was hoping I remembered correctly! :-)
Cheers Trevor Jones
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Hi Steve, it's definitely a 55 deg form, perfect fit on th
thread gauge, and just a shade over 0.500"but thanks for the info anyway.
UNS is the 'special' form over there isn't it -any particular purpose it gets used for?
From what I can tell is a constant pitch series a bit like our ol brass or ME threads
Steve Larne
-- Steve Larne ----------------------------------------------------------------------- Steve Larner's Profile: http://www.rcgroups.com/forums/member.php?u 733 View this thread: http://www.rcgroups.com/forums/showthread.php?te857
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On Sun, 18 Mar 2007 14:56:12 +0000, Peter Neill

I've got 3/4" & 1" conduit dies spare if they would help. No 1/2" though, & don't think I've got any taps.
Cheers Tim
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On Sun, 18 Mar 2007 18:14:54 +0000, Tim Leech

Thanks for the offer Tim, much appreciated, but I think I'll probably end up screwcutting them both. To be honest I'm quite looking forward to doing it it as I've been without the machines for 2 months now whilst the new floor has gone down, and have missed using them.
Peter
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