27 TPI 10MM tap?

[Bessy]

So here's the story, bought some hanging lights that hang over the bar in the kitchen. Once hung (they have a hollow cylindrical tube that's about 12mm or so in diameter), they hang too low. The plan is to cut one of the tubes in half, and retapping the ends to screw back into the mounts/lights on both ends.

The kicker is, that when I looked through my tap/die set, I determined that the thread I need is 27 TPI, and 10mm diameter, which ofcourse isn't in the kit I have.

Has anyone ever seen (know of a source) such a tap size, outside of a factory somewhere in the heart of Indonesia?

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[Bessy]

Sounds like M10x1.0 (25.4 TPI)

Now obviously the diameter is different, but I thought that, I tried matching it up with a M8x1 thinking it'd be close, but no go on the thread count.

The closest I found (and I'll admit I gave it a go and stopped when it bound up) was a 1/8-27npt die I had. It ran on nice and smooth for about the first 1/4 of an inch of thread, but upon trying a tester with the tap, it's a looser fit than stock. I did discern from that though that we are definitely talking 27tpi, right on.

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[wolf_from_wv]

So it's a metric diameter and inch threads?

Does it look like one of these?

http://www.antiquelampsupply.com/category/175_pipe-*******--rod

I see 1/4 - 27 all-thread...

http://www.antiquelampsupply.com/product/2104_steel-all-thread-solid-rod

Other info

https://www.homeownershub.com/maintenance/thread-for-standard-light-fixture-******-632913-.htm

https://grandbrass.zendesk.com/hc/en-us/articles/203607534-Thread-Size-Chart-

 

[bigdav160]

Threads per inch pitch does not work with metric fasteners

 

[Is0ld0ut]

10mm 1.25?

 

[Bessy]

sounds odd, I know. but it passed through the 10mm hole on my tap gauges, but bound up in the 3/8" hole. My next best guess is to try a 3/8-27 tap.

 

[Bessy]

10mm 1.25?

nope. it's very clearly a 27tpi thread, fits perfect on the gauges i have.

 

[Is0ld0ut]

I think you were asking about my response. 10mm bolts come in 1.0 pitch and 1.25 pitch. If the 1.0 wasn't correct might be a 1.25.
My cheap harbor freight rap die set came with a pitch gauge which is very hand for determing the right bolt/tap/die.

 

[bob15]

There is no such thing as a 27tpi M10 bolt. If it is 27TPI, then it is a SAE bolt. Metric, as stated above are 1.0, 1.25, 1.50.

Are you sure it isn't a 1/4-28 bolt (very common size)

 

[neophyte]

Any chance British Standard Cycle (BSC) might have been used?

Industries in different countries use weird or obscure standards sometimes. British Standard Whitworth is still used on some Asian made grinders and BSC is still used for bicycles.

https://en.m.wikipedia.org/wiki/British_Standard_Cycle

http://www.motalia.com/Html/Charts/cycle_chart.html

 

[LXCam]

There is no such thing as a 27tpi M10 bolt. If it is 27TPI, then it is a SAE bolt. Metric, as stated above are 1.0, 1.25, 1.50.

Are you sure it isn't a 1/4-28 bolt (very common size)

I'm with him. I think you have a jic fitting type thread. I'll be going into the shop in a little and confirm the size I think you have.

 

[Carla]

The old 1/8 NPS standard is commonly found in electrical work, particularly in lighting fixtures.

That '1/8' is a 'trade size', like the 1/8 NPT used in pipe fittings, and is purely 'nominal'.

The dimensions of 1/8 NPS, from the old 'Machinery's Handbook', are .404 max. O. D., and a pitch dia. of .3748/.3713., with 27 threads per inch. It would look 'close' to a 10MMx1MM pitch, but is not identical.

You should be able to get a 1/8 NPS tap 'off the shelf' from any good machinists' supply house. It won't cost much, and would be worth having on hand if you do any lighting fixture work.

cheers

Carla

 

[neophyte]

1/8" NPT is very close to the dimensions you specified.

1/8". Nominal Pipe Size (inch)

27 Number of threads per inch

0.405 Outside Diameter (inch)

10.287 Outside Diameter (mm)

 

[LXCam]

You sure you don't have a 3/8 x 24 or a 10 x 1.00.

 

[californiaHank]

It sounds like pipe thread.
1/8" pipe usually gets 27 tpi NPT fittings.
(The 1/8" designation doesn't refer to the outer diameter - the actual OD of the pipe is a tiny bit over 10mm. NPT stands for National Pipe Thread Taper.)
Any hardware store will have 1/8-27 pipe taps.

 

[wolf_from_wv]

1/8-27 NPS and not 1/8-27 NPT?

https://www.homeownershub.com/maintenance/thread-for-standard-light-fixture-******-632913-.htm

 

[KnurledNut]

The correct item you need is a 1/8-27 IP tap.

(IP stands for "iron pipe". This is also called IPS, or NPS as Carla mentioned.)

Here is a chart:

 

[Carla]

1/8-27 NPS and not 1/8-27 NPT?

https://www.homeownershub.com/maintenance/thread-for-standard-light-fixture-******-632913-.htm

I should have mentioned.......the 'NPT' in the old pipe thread specs refers to 'National Pipe Tapered', which is the common sort of pipe fitting thread which will seal to withstand pressure, owing to the taper of the thread. The common style of grease fittings, often called 'zerks', are usually either this thread, or the smaller 1/4-28, in which the 1/4 is actual diameter.

The 'NPS' spec is for the same nominal diameter as the NPT series, and the same number of threads per inch, but as a 'straight' thread, not tapered. This, in the old handbooks, is often referred to as a 'chandelier thread', and was commonly used in electrical work, particularly electric lighting fixture components.

Yes, its confusing.....but these thread standards go back into the 1880's and 1890's, when the commercial standardisation of thread forms and dimensions was just beginning to take place, and the 'trade practices' of different trades, such as those of the first commercial electrical equipment manufacturers, were adopted as standards.

So......the electrical manufacturers chose to use basic commercial pipe thread dimensions, but modified for straight threads.....it seems silly, the now, but one must remember that the now-common SAE fine thread series didn't exist, as a standard, at that time.

cheers

Carla

 

[Bessy]

Carla has hit it right on the head i think. It's an electrical fixture right, so it's not your typical pipe threading. As I mentioned before, the closest thing I could find was a 1/8-27NPT which ran good for a few turns then bound up. I gave it another turn or two just to see if it was a burr, but upon attempting to thread the connection (male threaded hollow all-thread) in, it was definitely a "looser" feel, leading me to believe that it's an ever so slightly larger diameter or different thread pitch.

 

[leg17]

Carla and Knurled Nut have it.

 

[PelicanPines]

First time I bumped into this exact problem (restoring an antique floor lamp)... I went to a local hardware store with a very nice old owner... who turned out to be CLUELESS to pipe threads...

Learned a lot since... If it's electrical... it's probably pipe threads...

Even the local LIGHTING place... WHO supply electrical supplies... were clueless as to threads etc...

So... you need the following ability to measure...

1. Metric...
2. SAE Fine...
3. SAE Coarse...
4. Pipe threading...

Never needed to and not sure if there is a good way to measure taper.

As soon as it fits a TPI or threads per inch... it AINT metric at all... is a good rule.

 

[Bessy]

Right, and I kindof knew that going in, but when i tried the thread gauges, it was bang on 27tpi, but it had to practically be threaded into the 3/8" hole diameter-wise and even then it was only like a turn and a half. wouldn't go any further.

 

[Roju1985]

Can you cut the tube in half, then thread the uncut thread in from the back side of the mount and thread it all the way down flush with the mount then you can spin the fixture in on the uncut side of the tube and not have to worry about the boogered threads on the cut side? Sorry if this idea is hard to picture via text.

I imagine this is what you are dealing with:

 

[PelicanPines]

Right, and I kindof knew that going in, but when i tried the thread gauges, it was bang on 27tpi, but it had to practically be threaded into the 3/8" hole diameter-wise and even then it was only like a turn and a half. wouldn't go any further.

Yea... the outside size for things PIPE threaded are strangely measured... it seems to be 3/8" but that's like a totally different nomenclature in PIPE threads... so you can't go for 3/8" NPT...

None of what I say is exact but just an example of "Yea been there... got annoyed too"... just file it away with ... OK this is PIPE thread maybe.