1/2" x 18 TPI thread?

I believe 1/4 NPT is about 1/2" o/d x 18 tpi

1/4" ANP is 0.540 x 18

Conduit is 1/2" x 18

-- Regards,

John Stevenson Nottingham, England.

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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

Is it whitworth form as there is a 1/2" x 18 TPI anerican UNS thread

0.490 over major Dia

Steve Larne

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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

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

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

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 -

1. 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.

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

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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

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

Steve.

It's allright! I was hoping I remembered correctly! :-)

Cheers Trevor Jones