# CO2 cartridge thread



## phreeky (Sep 25, 2015)

I'm attempting to make a bracket to hold some CO2 cartridges and an inflater however I'm stuck - the thread on them seems odd. Googling tells me they're 3/8-24 however that doesn't seem right - using my tap to create a bracket, the cartridges seem a bit loose. The thread pitch appears correct however.

It's almost as if they're actually an M9 thread with a 1mm pitch, but that seems unlikely. Putting the callipers over the thread on the cartridge gives 9.00mm exactly.

Does anyone know for sure?


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## phreeky (Sep 25, 2015)

More research suggests that this is a specific pipe fitting size, however it doesn't appear to be tapered. Certainly not 3/8-24 as one CO2 supplier website suggested.

edit: I'm thinking this may be 1/8 BSPP or something like that. This isn't as easy as I thought!


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## Cleared2land (Aug 31, 2012)

I use un-threaded cartridges, so, I can't be of any assistance there, but I would be interested in seeing a photo of what you're fabricating.


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## phreeky (Sep 25, 2015)

Well the one hacked job to test dimensions/clearance is horrid and chopped up now, however I'm essentially making alternative use of the front derailleur mount (as I'm running a 1x). It places them behind the seat post, so I had to drop the air from the rear shock and bottom it out to ensure that the tyre and arch between the seatstays don't come too close.

I believe that 2x16g cartridges and the inflator should fit OK - with a tube, levers and multi-tool mounted elsewhere then it may allow me to free myself of the camelbak for shorter rides or places where I can top up the water bottle.


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## Kbarrette (Mar 16, 2013)

phreeky said:


> More research suggests that this is a specific pipe fitting size, however it doesn't appear to be tapered. Certainly not 3/8-24 as one CO2 supplier website suggested.
> 
> edit: I'm thinking this may be 1/8 BSPP or something like that. This isn't as easy as I thought!


If you are finding they are a bit loose then there is a very good chance they are NPT thread. There is a slight taper so the more you screw in then thread it will seal the threads and get tighter. That's most likely the reason for your wobble.

Sent from my iPhone using Tapatalk


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## Slash5 (Nov 27, 2011)

Don't have Google?
Frequently Asked Questions | Genuine Innovations

What is the size of the threading on threaded GI CO2 cartridges?

Our cartridges are standard threading (3/8", 24)


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## phreeky (Sep 25, 2015)

Like I said in the OP, I've googled and found that, however unless my tap+die set is all out of whack (it's a cheapy as I avoid imperial like the plague, but still not likely) then 3/8-24 doesn't appear to be correct. Googling more suggests that it's more likely to be a standard used for gas/liquid piping (NPT, BSPT, BSPP, CGA etc), and these don't appear to be tapered and so that rules out some.

I'm thinking it's therefore probably BSPP 1/8-28 or some CGA thread. I'm not sure I could be bothered to go spending more money on taps as a gamble so will have to attach them via other means.


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## Slash5 (Nov 27, 2011)

I just threaded a CO2 cartridge into a 3/8 NF die without any problem - screwed in like it was made for it.
I find that usually taps and dies make a loose fitting thread. Try drilling the hole undersize for a smaller root. Or make your bracket thinner and put a jam nut on top, finger tight.


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## wschruba (Apr 13, 2012)

Slash5 said:


> I just threaded a CO2 cartridge into a 3/8 NF die without any problem - screwed in like it was made for it.
> I find that usually taps and dies make a loose fitting thread. Try drilling the hole undersize for a smaller root. Or make your bracket thinner and put a jam nut on top, finger tight.


Tapping an undersize hole is a great way to bind/break a tap. Be careful...


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## phreeky (Sep 25, 2015)

Maybe my tap+die set really is junk.

I tried the undersized trick already (in alu, using some lubricant so low chance of a break) and it was still way too loose.

I think I will just deal with an alternative method  Thanks for the input though.


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## SpartanH (Jul 12, 2018)

You should try making a silicone putty around an old cartridge to match the treads. If your trying to make it air-tight, be sure to use a slow reacting catalyst and put the mixture in a vacuum chamber.


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## wesMAmyke (Nov 12, 2005)

Here is a co2 pierce adaptor for threaded cartridges, lists the thread as 3/8x24 UNF. I would tend to trust whatever they list the thread as, co2 stuff is all they do.

https://palmerspursuit.com/products/16-gram-to-1-8-npt-adapter


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## RonSonic (Jan 8, 2005)

Put a 3/8" O-ring on the cartridge and let it act as a springy lock washer to hold it in? Maybe a couple turns of plumber's tape around the threads?
I like this idea.


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## life behind bars (May 24, 2014)

Invest in a good tap and the correct drill.


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## Stalkerfiveo (Feb 24, 2015)

The cure for your headache is only 12$ I have one on my XC bike and love it. Doesn't interfere with my Bontrager sideswipe cages or the bottles going in/out.

Positz Dual Co2 Cartridge Holder... https://www.amazon.com/dp/B01E6SMMZC?ref=yo_pop_ma_swf


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## Codemonkai (Aug 16, 2021)

phreeky said:


> I'm attempting to make a bracket to hold some CO2 cartridges and an inflater however I'm stuck - the thread on them seems odd. Googling tells me they're 3/8-24 however that doesn't seem right - using my tap to create a bracket, the cartridges seem a bit loose. The thread pitch appears correct however.
> 
> It's almost as if they're actually an M9 thread with a 1mm pitch, but that seems unlikely. Putting the callipers over the thread on the cartridge gives 9.00mm exactly.
> 
> Does anyone know for sure?


I have a thread checker for a 16gram co2 cylinder that I have. The thread is 24 G or 3/16. Must be a whitworth thread.


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