FYI regarding non "AN" fittings

[szicree]

I know a while back we had a thread about unmarked AN fittings being shipped by Vans (I think) and Spruce. I also remember that the main concern was metallurgy and burrs. Well today I had an interesting conversation with a guy who makes "AN-type" fittings for hotrodders. He started out by explaining that the big difference between the real stuff and his stuff is the documentation. This I knew. He went on to tell me how the real stuff has rolled threads with radiused bottoms, whereas his stuff has cut threads with very sharp bottoms. I guess I expected this. Finally, he told me how he drills the inner bore of his stuff slightly oversize to flow better. The difference was slight, but you can definitely see it. Don't get me wrong, the guy's a good guy and produces very nice work, but I gotta figure that cut threads combined with reduced wall thickness makes for a significantly weaker part. Since this stuff only carries highly flammable gasoline to the single engine of the airplane that I ride in, it shouldn't be a big deal, right?

[asav8tor]

316 Stainless Steel.

Used on things that go into outer space.

http://www.sspfittings.com/products/...e.asp?brand=26


http://www.sspfittings.com/products/...y=all&brand=26

[captainron]

Originally Posted by asav8tor

316 Stainless Steel.

Used on things that go into outer space.

http://www.sspfittings.com/products/...e.asp?brand=26


http://www.sspfittings.com/products/...y=all&brand=26

Just think of all the vibration that goes on in outer space!

[az_gila]

Originally Posted by captainron

Just think of all the vibration that goes on in outer space!

Ron... if you have watched a piece of equipment you have designed on a vibration table getting the NASA launch vibration qualification levels, you would be amazed at the motion involved....
It was so much, my boss could not stand to watch it, he just went home (for a stiff drink, I think.......)

It might be OK in space, but it sure gets shaken up getting there....

gil A

[captainron]

Originally Posted by az_gila

Ron... if you have watched a piece of equipment you have designed on a vibration table getting the NASA launch vibration qualification levels, you would be amazed at the motion involved....
It was so much, my boss could not stand to watch it, he just went home (for a stiff drink, I think.......)

It might be OK in space, but it sure gets shaken up getting there....

gil A

I was just having some fun, Gil. I used to work with a lot of 316 stainless in pharmaceutical industries; it was a metal that was pretty soft and would easily gall, or transfer metal when threaded to another 316 piece. I had an early stainless automatic pistol that got real sloppy when galling occurred between the slide and frame. Stainless seems to be fine when mated with aluminum or steel. I just never liked the stuff real well.
Regards, Ron

[52Pop]

Hi Steve, You are on target here. Cut threads will have sharp non-radiused bottoms, as well as the on the tops of the threads. This is the standard machine shop way of doing things, faster and cheaper. I would not use cut threads on something like this. You radius edges and corners on sheets and angle stock for a reason. It still applies to that as well with threads. Go with the rolled threads if possible. And as you said, this person enlarges the opening for better flow. That means thinner walls, which also means less strength with cut threads. Good luck!

[G-force]

My day job deals in manufacturing and machining, so let me make some clairifications. The shape of a thread has little to do with process it was made with. The root and crest of a thread form is dictated by the thread specificationit is being made to, be it cut with a die, single point, rolled or ground. AN grade fitting threads have to meet the specifications laid out in the drawings and specifications. Tolerances must be met, and processes may be specified. I agree, some of the non-AN complient "automotive" fittings are of a lesser quality, however not all, and it usualy is not due to the method of applying threads.

[szicree]

Thanks for the clarification and I would agree that some auto stuff is of high quality. The real point of my post though was that it is darned close to impossible to tell by looking what the thread profile is, how they were formed, and whether the bore has been enlarged. Obviously the alloy/heat treatment used cannot be determined either. The fact is that the auto stuff could be of the absolute finest quality, but unfortunately there is no way to tell, so I'll avoid it.

[az_gila]

Originally Posted by G-force

..... I agree, some of the non-AN complient "automotive" fittings are of a lesser quality, however not all, and it usualy is not due to the method of applying threads.

It appears that there are quite a few differences between the SAE fittings ad the true AN fittings (and their later AS specifications...)
The thread making method may not be specified, but the final threads are different, including "radiused root threads"

This note from a reputable manufacturer that makes both types is quite interesting...

http://www.parker.com/tfd/fittingsol...ANFITTINGS.pdf


gil A

[G-force]

It appears several changes have been made over the years. Going from a class 3 to 2 is basicaly allowing for a sloppier fit. The thread profile also appears to have changed from UN to UNJ. I'm curious how this affects the current AN/MS specs as I believe they have switched to an SAE spec. But I cant imagine them going to a sloppyier fit and less desirable thread profile. I wonder how old the Parker PDF is, the specs it lists for AN fittings are no longer active.

Originally Posted by az_gila

It appears that there are quite a few differences between the SAE fittings ad the true AN fittings (and their later AS specifications...)
The thread making method may not be specified, but the final threads are different, including "radiused root threads"

This note from a reputable manufacturer that makes both types is quite interesting...

http://www.parker.com/tfd/fittingsol...ANFITTINGS.pdf


gil A