Different Color AN Fitting?

tx_jayhawk · #1 09-19-2006, 08:39 PM

Anyone else seen an aluminum AN fitting like this? I bought some at my local aircraft supplies store (B&B), and they are supposed to be the same as the regular blue ones. It is even stamped with an "AN 818" on the side.

I understand that these particular pieces came from McDonnell Douglas. I was told the reason they are anodized a different color is that they are used in oxygen fittings. The different color anodizing is apparently done, as they have different sterilization requirements (i.e. they are kept cleaner).

Wondering if anyone else has seen or can confirm this understanding (curiosity).

Thanks,
Scott
7A Finishing

G-force · #2 09-20-2006, 12:27 AM

I know Goodridge and probaly others (Russel, Earls, etc) do finish them in black, and a clear/pewter anodize. Pretty common in the High Perf automotive world...I dont know if all of them are aviation grade and marked as such. The finish, reguardless of color, is the same type II anodize so performance wise, it is the same. The machine shop that machines all my fitting for my work does alot of AN fitting for a large supplier (Neilson I believe) and the difference in the Aero grade is accountability of the material and tolerances. All the marking are roll stamped on the hex stock when it is still a 12 footer, and material certificates from the mill must follow the batch of parts the whole way.

az_gila · #3 09-20-2006, 09:43 AM

Is it aluminum?
Some different materials might have ben selected for Oxygen (if that story was correct)... could it be brass or inconel?
The AN stamp means is is made to AN specs, but doesn't say what "dash number" of the spec.... the steel and aluminum AN 818s are all stamped the same...

gil in Tucson

tx_jayhawk · #4 09-20-2006, 11:58 AM

Gil,

It's definitely aluminum. I can't discern a difference except for the anodizing color. I generally trust the source (&B Aircraft Supplies), but I was hoping someone on the list would be able to vouch for the background info I was provided.

Scott

az_gila · #5 09-20-2006, 01:34 PM

Scott.... the AN818 spec is on-line here...

http://assist.daps.dla.mil/quicksear...t_number=54315

The only materials acceptable for the AN spec. are
Steel
Aluminum Alloy
SS 304
SS 316
Titanium Alloy
7075 Alum. Alloy

Each one has a dash letter, except for steel.... are there any letters stamped on the part?

Interestingly enough, the AN Spec. does not specifiy color, so all of the anodized colors on aluminum could still be considered conforming parts... there seems to be nothing special about blue....

UPDATE... in the move away from MIL-stds to commercial standards, the generic 37 degrees fittings seem to be now covered by AS4841, an SAE document - no on-line link, it seems to be $71+ from the SAE....

However, I found a copy at work, and the fittings are color coded...

This is the code...

a. Aluminum alloys 2014 and 2024: Blue
b. Aluminum alloy 7075: Brown
c. Steel: Black
d. Copper-base alloys: Natural cadmium
e. Corrosion-resistant steel: None
f. Titanium alloy: Gray

Seems to be valid for all fittings made after 1995 - and probably before that, but I can't confirm....

Do you have a Brown one, made from a stronger 7075 alloy??

gil in Tucson