G 1/4 and 1/4 NPSM are not that similar

I've seen a lot of post with this misconception so Just to let everyone know there is a large difference in a G ¼ thread and a ¼ NPSM. There is more to a thread than the pitch diameter and the TPI. I personally would not put a ¼ G in a ¼ NPSM. yes you can get it to work but at what cost.

Most obvious but not most important is the 18 TPI and 19 TPI.

There are two other major difference.
One of the biggest difference witch I fined interesting no one who sells these fittings mentions is the G 1/4 witch is a British has a 55 deg. Included angle and the 1/4 NPSM has a standard 60 deg. Included angle.

The second major difference is the G ¼ is supposed to have a full radius on the crests and valleys of the threads.

If you add up the differences between the two you have some major issues. They do fit together because the G1/4 is short. But when you factor in the differences and the length of the G1/4 you have very little thread engagement. And when you put enough torque in the fitting to actually seal, even with Teflon tape I can guaranty that metal G1/4 fitting is in some way damaging the Delran thread in your storm or other Swiiftech product with ¼ NPSM threads in it. I put a couple links with the spec for British and NPSM threads.



G 1/4/ (British threads)
http://www.gewinde-normen.de/en/whitworth-pipe-thread.html

¼ NPSM
http://www.rjsales.com/products/nipples/tab6.gif

I made My own barbs but unfortunately not everyone has the means and I have not found a good replacement for the plastic ones

I couldn't agree more! I didn't really realize the difference myself until you said something and I started looking into it and I was amazed that they would sell a barb with a british thread for an american internal thread. I guess if you put enough teflon tape on the thread it's going to seal but it's definitely a massive mismatch in threads. I think the pictures in the links tell the story.

Yes, they are not very similar but they WILL work just fine.

Take swiftech's products for example. They use NPSM which is a parallel fitting.
G1/4 fittings like the EK and DD barbs will fit on them as well as the O ring will go into the groove (on the block). In addition, even Swiftech's high flow barbs use G1/4:
http://www.petrastechshop.com/swhifig1th1o.html

And when you put enough torque in the fitting to actually seal, even with Teflon tape I can guaranty that metal G1/4 fitting is in some way damaging the Delran thread in your storm or other Swiiftech product with ¼ NPSM threads in it. I put a couple links with the spec for British and NPSM threads.

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In the world of plumbing, fittings are meant to go in once, then never touched again. Every time you take off a fitting and put it back in, you are damaging the threads. This will happen no matter what you do.If you put the fitting in once, then leave it there you will be fine.

I am not discrediting your information because it is true but I am pointing out that you can use it and it is not "bad". As for those barbs you have in the picture.... where can I get them? They are so damn nice.

Tyreal said:

In the world of plumbing, fittings are meant to go in once, then never touched again.

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True, but in my world I upgrade and change hardware constantly so my system never stays in tact.

Same here, but I don't constantly take off fittings. Even if I'm cleaning the block, I don't remove the fitting, I will just take apart the block to clean it.
(By fitting I mean, the barb)

Yeah, I know. I guess being a machinist it's a little like putting a square block in a round hole to me. It will fit with enough force! I'm just surprised they don't make the right fitting for it. I'll be putting my stainless barbs in this weekend.

Cool. Did you make these barbs yourself?

Yea I know where your coming from with this. I think it's more like putting a slightly less circular block in a round hole.

Tyreal said:

Cool. Did you make these barbs yourself?

Yea I know where your coming from with this. I think it's more like putting a slightly less circular block in a round hole.

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Yeah, we had a buddie of ours make them on a Swiss CNC Lathe. I'm a milling man so I leave the round stuff to those guys.

Awesome. If you can I'd love to see some pictures.

Relative to the original topic... I just bought some Danger Den High flow G1/4 to 1/2 barbs and I am going to use them on my MCW60 and Storm.

Scorpiontl is designing a cpu water block right now, he has most of it drawn up. Hopfully I'll start machining soon, we'll get some pictures of that as we go. If you want I'll ship you a couple of those SS barbs if you want to try them.

Send me a PM or IM and we can talk. It's against the rules I think to discuss in here.

Tyreal said:

Send me a PM or IM and we can talk. It's against the rules I think to discuss in here.

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Only if I sell them, i'm giving you a pair. PM on the way.....

Thanks for providing the information. I will be bookmarking this page .

f you add up the differences between the two you have some major issues. They do fit together because the G1/4 is short. But when you factor in the differences and the length of the G1/4 you have very little thread engagement. And when you put enough torque in the fitting to actually seal, even with Teflon tape I can guaranty that metal G1/4 fitting is in some way damaging the Delran thread in your storm or other Swiiftech product with ¼ NPSM threads in it. I put a couple links with the spec for British and NPSM threads.

Click to expand...

Thats part of the reason I like using RTV Silicone. It's more likely to compress and be forced out of the area. I see this problem all the time with threaded pieces at work. I always keep the tap and die handy. "Should work" is never a good answer when you're working with $250 knives, let alone a $1000 sword .

Not the usual damage I see to knives is not a broken blade but a damaged threaded hole where a metric screw was used where a 4-xx screw should have been used or vice versa. Sometimes it works for a month or so until it gets stripped or the next time the part in question needs to be disassembled for maintenance it ends up being locked in place.

Edit: redundant participle

I don't check my post for an evening and i miss all the fun. dylskee pretty much said anything I would have. one thing I would like to add is a NPSM thread with an o-ring is a designed that can be repeatedly assemble and disassemble without causing damage. anytime you use a fitting with a tapered thread (NPT) you are talking about a thread that does damage when you torque it down.

One thing I have to admit witch dylskee led to a bit is being a machinist we are very picky and particular about mechanical components and things that will be functional but not correct is just not good enough for us.

SCORPIONlt1 said:

One thing I have to admit witch dylskee led to a bit is being a machinist we are very picky and particular about mechanical components and things that will be functional but not correct is just not good enough for us.

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Translation: Machinists are usually obsessive perfectionists.
I should know

Ahhh, fellow machinist . Couldn't have said it better myself.

I can agree with that