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BSP vs NPT vs "PT"

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Eddy Curr10/12/2019 19:48:31
39 forum posts

- Will 1/8" NPT male thread seal in 1/8" BSP female thread. (I am aware of the flat/rounded shape and 60/55 angle differences between the thread types.)

- What is "PT" as regards to products mfd in China.

- Are there 2-3 UK or other sources for small BSP fittings. In particular, 1/8" BSP hex plugs.

I am located in Can where NPT is the norm. I can across a solenoid valve suitable for a project of mine - unfortunately, it has 1/8" BSP female ports as listed by most vendors. A few vendors offering the same valve describe the ports as 1/8" "PT".  So far, I have not come across an equivalent valve (2-position, 3-way) w/ NPT ports and a solenoid configuration suitable for the application in mind.

I have seen 1/8 "PT" Push-to-Connect hose fittings paired with the valves. These do not appear to meet my needs because: a) I don't know what PT thread is and b) I intend to use bespoke barb fittings (hex plugs drilled for 3mm OD brass tube.)

I have discovered one 1/8 BSPM - 1/4 NPTF adapter: the price is high for my purposes. Together with the matching NPT fitting, this arrangement is a deal-breaker.

Edited By Eddy Curr on 10/12/2019 19:53:59

JasonB10/12/2019 19:52:18
18278 forum posts
2022 photos
1 articles

Pitch of the two threads is also different so unlikely to fit NPT is 27tpi and BSP is 28tpi

Eddy Curr10/12/2019 20:03:57
39 forum posts
Posted by Eddy Curr on 10/12/2019 19:48:31:

... I can across a solenoid valve suitable for a project of mine

I tried to edit the previous post several times, but the post text failed to display longer than momentarily before disappearing - seemingly a result of slow-to-load advertising banners. I'm all in favour of advertising - right up to the point where it bogs down the site and interferes with key functionality.


The previous content should say "... I CAME across ..."

JasonB10/12/2019 20:08:21
18278 forum posts
2022 photos
1 articles

Eddy you should be able to get 1/8BSP or G1/8 plugs from e-bay, just use rather than which will tend to give mostly NPT results.

Eddy Curr10/12/2019 20:08:45
39 forum posts
Posted by JasonB on 10/12/2019 19:52:18:

Pitch of the two threads is also different so unlikely to fit NPT is 27tpi and BSP is 28tpi

Hmmm. Different pitch, form and angle?

Probably nothing that additional PTFE tape and a bigger spanner can't fix, huh ?

Any forum vendors with a line of small BSP fittings that trade overseas ...

Eddy Curr10/12/2019 20:15:43
39 forum posts
Posted by JasonB on 10/12/2019 20:08:21:

Eddy you should be able to get 1/8BSP or G1/8 plugs from e-bay, just use rather than which will tend to give mostly NPT results.

Thank you. Yes, I've had success w/ searches on in the past, too. Thought I'd ask about preferred vendors here as I've had pleasant dealings w/ the likes of Arceuro and others in the past, just don't know who carries such fittings.

G1/8 is a new term for me. Can you elaborate a bit?

Eddy Curr10/12/2019 20:33:42
39 forum posts

Bit of hex brass stock and a little set-up. Given the same amt of time I've put into the BSP-NPT issue, I'd probably already be finished the 20 or so hex plugs.

Just seemed like there should be a readily available commodity: valve w/ NPT ports; easily-available BSP fittings.

Thank you. I'll get on with it ...

Howard Lewis10/12/2019 21:25:08
3361 forum posts
2 photos

Correct Eddy!

NPT will be 60 degree thread form, while BSP will be 55 degree Whitworth thread form; as as you now know the pitch also differs.

By the sound of it you need more than just three for one solenoid valve? You would need a 1/8 NPT die (assumes that the valves have female ports ) and a 1/8 BSP tap to produce the female part of the adaptor.

Otherwise, i would advocate getting some hexagon brass bar and making your own adaptors, unless you want to go into mass production?


SillyOldDuffer10/12/2019 21:29:08
5901 forum posts
1280 photos

Comprehensive list of threads here on The Engineering Toolbox. I hope no-one expects a short simple list!

PT was a Japanese Industrial Standard thread. It's interchangable with BSPT.

PF was the JIS thread interchangable with BSPP (parallel), and later called 'G'


Edited By SillyOldDuffer on 10/12/2019 21:29:25

Philip Powell10/12/2019 22:12:18
66 forum posts
15 photos

The "G" denotes Gas thread, interchangeable with BSPP


David Davies 810/12/2019 22:42:04
110 forum posts
8 photos


ISO 7 defines European pipe thread standards which as far as I can see copy the BSP 55 degree form, pitch and diameter. The standard prefixes the pipe diameter with a G. For example G5/8 is 5/8 BSP. This size is the European standard for a scuba diving cylinder exit port thread. A strange case of a non metric thread being an ISO standard.

So G 1/8 is 1/8 BSP by another name.



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