Imperial thread


I have a trivial question. I messed up half the thread on the vapour port of the recovery cylinder I use to stock up my solvent in between runs. I think I can use a long female female coupling then a reducer then a 1/4 npt to jic bit (or directly a reducer if the female part is long enough).
However I’m a bit confused by those imperial threads and while I thought everything was in 1/4 on my CLS, 1/4 jic and 1/4 FL seem a tad smaller.

So my question is:
If I’m using 1/4 jic tubing and my recovery cylinder is 1/4 fl-m should I chase a 1/8 (+/-9,5mm) npt female coupling?

I’d like to avoid ordering unusable parts from far away.

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1k word substitutes (pictures) are gonna make this easier….


I’m on holiday so I can’t take a pic of my rig ATM but I do have a pic of th f up cylinder.
I have a pretty basic 1lbs Chinese CLS with 1/4 line, 1/4 npt parts.

Connections are 1/4 fl-m according to the seller.

I don’t use teflon usually but was trying to find a solution with bits I own. I know it’s a no-no with jic.

I’d like to use the following parts



Tank is supposed to be 1/4 fl-m but 1/4 npt is too big. Outer diameter of the thread is more or less 9,5mm wich I assume is 1/8". That’s where I’m confused why call it 1/4 fl-m when it’s smaller that 1/4 not. I’m wondering if there’s more subtilities with Imperial thread.
I don’t know if it makes more sense between my lack of knowledge and my terrible English.


The problem is that if your vapor port threads are messed up and you cant properly connect your hose, that an adapter will also not properly thread to your tank vapor port, no?


Probably but I’ve still have half the thread ok. So I hope to be able to find a long female female bit that could grip on the ok thread. That’s why I’m trying to understand what imperial size I’m after.

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Your tank has straight threads.

NPT is by definition tapered.
Your proposed solution is not even close.

Tank hads 1/4” SAE flare, which isn’t really the same as 1/4” JIC (different taper). At 1/4” they are considered “close enough”.

So you looked at the specs?!?



The Similarities and Differences Between JIC and NPT Fittings

I can relate I did the same back in the day, those ports are weak as fuck, stripped one and broke another clean off.


Does your tank have an extra plugged port?

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Damn I had no idea there was so much differences between threads. I thought everything was straight and that diameter, connections and eventually “teeth” specs would differ. You sirs get me a bit of reading. I’ll dig into that.
Thanks a lot

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Unfortunately no

Best bet is to replace the entire valve (see up thread)

Although that is approaching 50% of the price of a new tank.

Any other solution (I can see) is just asking for trouble.

Which is not recommended in this game