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Threads used on electrical brass fittings

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Speedy Builder519/07/2019 12:29:32
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What threads are used on electrical fittings, between a lightbulb socket and a tubular brass support bracket. I am trying to help out a friend (By telephone) who has a 14mm OD thread which is not metric fine, but still a fine thread which goes into a larger light fitting. I have see somewhere that the thread angle may be 80 degrees.

Any ideas out there please ?

BobH

JasonB19/07/2019 12:38:54
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PG conduit thread maybe

Speedy Builder519/07/2019 12:57:25
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thanks Jason, PG are 80 degrees but not a 14mm OD (There is a 14mm cable size though). The 80 degree bit may have been just an idea I had. These fittings are often found on thin brass and steel fittings.

The light fitting in question was bought in London, wholesaled from USA and made in China ! What hope have I got of telling my friend what thread he has ?????

Robert Atkinson 219/07/2019 13:01:04
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No real standard. As Jason says PG is not uncommon, mostly on industrial fixtures though. Brass holders commonly have 10mm x 1.5, 20mmx 1.5 or 1/2" x 26tpi which does not seem to fit your description. Quite possibly some odd pipe thread.

Robert G8RPI.

JasonB19/07/2019 13:03:11
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Are you sure it is not 1mm pitch, a lot of the smaller size electrical stuff is 1mm pitch eg M10x1

14mm is also quite close to 9/16 x 26 or 20 tpi

Keith Rogers 219/07/2019 14:07:29
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Back in the day when I repaired chandeliers and light fittings I came across all sorts of threads.

Most fitting tended to be Brass thread , 9/16 x 26 BSB is 14.2mm OD so as Jason says is a very likely candidate.

Electrical conduit threads are based on american national pipe pitches, so 1/4 NPT would be .540" OD (close to 14mm ) but is 18t.p.i which sounds a bit coarse for the OP.

Later fittings were mostly Metric, again as Jason says 1mm pitch being common. Alth'o being from the US I would think that less likely.

Keith.

p.s. Sorry for the acronyms devil

Speedy Builder519/07/2019 14:13:30
1791 forum posts
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9/16 x 26 sounds about right, I will give my friend a ring. Anyone live in Lowestoft with a 9/16 x 26 BSB tap ??

BobH

Sandgrounder19/07/2019 14:14:26
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There is a 'British Brass' thread which is exactly 14mm dia, actually 0.5512" and at 26TPI very close to 1MM pitch.

from Machinery's Screw Thread Book.

Edited By Sandgrounder on 19/07/2019 14:15:34

Edited By Sandgrounder on 19/07/2019 14:17:22

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