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A place where restoration project-type threads can go to avoid falling off the main page in the WIX hangar. Feel free to start threads on Restoration projects and/or warbird maintenance here. Named in memoriam for Gary Austin, a good friend of the site and known as RetroAviation here. He will be sorely missed.
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Plating on AN and MS fasteners

Wed Dec 17, 2008 3:30 pm

I did a search of this and didn't see it previously covered.

I have been noticing that AN fasteners are usually yellow Cadmium plated.

As they age they rust. But amazingly enough the aluminum and other alloy fixtures they are securing do not seem to corrode like a similiar situation on a car.
This also happens with the Dzus fasteners on TEXAS RAIDERS cowls. They show signs of deep red, etching rust on the steel part, but the aluminum they mate against shows no signs of corrosion.
I'm not complaining, mind you.

Is the plating designed to act as a sacrificial cathode?


Wed Dec 17, 2008 5:13 pm

The cadmium is a sacrificial anode. The gold iridite I think is just a later, additional protective coating.

P.S. Stainless steel fasteners should not be used in contact with aluminum, despite what many Bonanza owners do (stainless steel screw kits). Plain carbon steel fasteners are closer to aluminum on the galvanic corrosion chart. Of course if your goal is to save the easily replaceable and inexpensive screws at the expense of the very expensive aluminum and magnesium parts, good on you!

Wed Dec 17, 2008 5:32 pm

Cad plating is dull silver, the golden color is the iridite coating which makes it look pretty. Either the dull silver or the golden color is good. I still have a test plate I cad plated about ten years ago, the one inch square area that is cad plated is still good, surrounded by rust.

Fri Dec 19, 2008 2:56 pm

Thanks for the info.

A lot of our hardware is still 1945 original and some of it has surface rust.
All the nasty stuff will get changed for new.

Fri Dec 19, 2008 4:19 pm

For steel parts I buff off light surface rust with a wire wheel and dip in thinned boiled linseed oil for protection. Seems to work well on interior items that won't be exposed to the environement. Other parts I buff and paint with a coat of clear on the outside to seal.

It just doesn't make sense for me to replate 5 or 10 pieces at a time and if I disassemble the entire plane and throw everything in a bucket to replate I'll never figure out how to put it back together. For common AN nuts and bolts (or anything critical like engine mount or wing bolts) I just replace with new.

Sat Dec 27, 2008 12:09 pm


That's some good advice you are giving on hardware.
You feel like giving hardware tours on Saturdays down here ? LOL :lol:

Kudos on the Stainless advice too.... I see that mistake being made everyday down here....


Sun Dec 28, 2008 2:17 am

Earls wrote:BDK

That's some good advice you are giving on hardware.
You feel like giving hardware tours on Saturdays down here ? LOL :lol:

Kudos on the Stainless advice too.... I see that mistake being made everyday down here....

Sponsor my T-6 resto with free hardware and I might be able to do one Sunday a month! :wink:

Saturdays are my T-6 work days and I don't accomplish enough as it is. I sure would like to visit some day though just to smell the history of all that hardware!

Fri Jan 02, 2009 11:23 am


Yeah there are some cool historical artifacts being found amongst the hardware. All kinds of Documents, Receipts, Employee Yearbooks, Etc. We even found some vintage girlie magazines. Times were different then.....

Tom Neely

Fri Jan 02, 2009 2:18 pm

What year, as close as possible, did they switch from A; clear cad to gold, B; from clear anodize (or the gray anodize) to blue on AN fittings?


War time fuel line, the red line ID is painted and the AN Fitting is clear anodize. I know the Dottie Mae had some blue fittings, but no gold cad.

Cadmuim and Anodizing

Fri Jan 02, 2009 4:12 pm

Seafury1 wrote:What year, as close as possible, did they switch from A; clear cad to gold, B; from clear anodize (or the gray anodize) to blue on AN fittings?

War time fuel line, the red line ID is painted and the AN Fitting is clear anodize. I know the Dottie Mae had some blue fittings, but no gold cad.

First, all my data is backed up from original blueprints and AN drawings that go back to the 1920's to the 1950's.
OK, Cadmium is only silver looking in its raw state. Class 1 refered to as ClassI is natural silver color. There are 2 variations on this, left raw and clear alodined. The first if left raw will start the corrosion process sooner that the clear alodine, which is done for just that reason. If you see hardware that is a dull gray color chances are if its new then it was not cleared. What is sooner, depends wildly on the environment, on a ship at sea, FAST, in a temp controlled hangar in Calif, probably not my life time.
If you want that gold color you still do the above, then use a colored dye, like Gold alodine for example. Technically its dyed with just a dye but you can use alodine.
There is no set date that I can come up with that is the magic day to start using ClassII(gold). I know for a fact from several Corsairs that ClassII was used during the 1945 time frame during manufacturing. We know this because several of us have removed hardware from deep within, painted over that was gold. Also it might take a few years for one vendor to go thru all the ClassI where another one might have ordered smaller amounts and used it up quicker. Who knows!

Anodizing is clear, period! Now before you say anything you must know how its done(I do it here in my shop as well as CAD plating, have been for 10 years).
Anodizing is the "growing" of a chemical surface on aluminum. Its actually done exactly opposite as Cad plating, except it uses ONLY chemicals. It looks like a Bee's honey comb under a microscope. AFTER the anodizing is done, it is then soaked in a dye of your choice. That dye fills the pores. Then it MUST BE SEALED to retain the dye. You do this by simply hanging the part over a steam of distilled water for a time frame. The combs just glaze over and curl up, sealing the dye in the anodized pores you "grew" on the surface. If the item looks Grey, it might just simply be natural aluminum looking, i.e. no dye. SeaFury1 your picture could have been blue at one time, its VERY LIKLY that the blue dye is simply gone.
You can check the integrity of an anodized part, put a volt meter on the item, it will NOT conduct electricity. If it does the anodized surface has broken down. This is usually seen from the dye either missing or very very faded. Once the anodizing is gone, it can start corroding.
As for the time frame of Blue AN fittings, I can tell you the AN "Print" says it was approved in 3 Feb 1941 for an AN815 Union. You would have to look deeper on the print for the Proc Spec to describe the finishes and other info. In this case it is MIL-F-5509. This print I have was last revised 1 June 1954. After that I dont know or care as I am stuck in the 1940's !
Which brings us to another subject, who used what when. The US NAVY required AN fitings as early as 1942. There is a slight variation of AN fittings from 1942 to 1955, but as far as I can find it was mostly machining variations, the prints dont really change the basic measurements.
So is it ARMY or NAVY, seems they didnt really do the same thing most of the time. Kinda like ARMY vs NAVY football. Need I say more!!
So the question is do you use Steel, brass or aluminum AC or AN fittings on a restoration, are they CadI, grey, blue or black...
Do you use ClassI or ClassII hardware...
Do you use SS clamps or steel, again, plated ClassI or ClassII...
and on and on...
DEPENDS ON TO MANY VARIABLES! I have lost countless hours of sleep trying to decide on things like this.
Chuck Wahl
Last edited by t28pilot on Fri Jan 02, 2009 10:53 pm, edited 1 time in total.

Fri Jan 02, 2009 6:16 pm

There is no evidence of corrosion on the B nut, and I have not stuck an Ohm meter on it yet. That is quite a bit of info and I appreciate it. I do have another fuel line that is from the same era but I can't confirm it was manufactured in the 40's. It has a blue anodized B nut on a Brass sleeve (AN819-6) I thought this was interesting. I'm pretty sure the one pictured is original clear. I assume your shop is in NorCal Also. What's a good price for doing a box (around 15 to 20 pounds) of steel misc hardware Class I?


Fri Jan 02, 2009 11:16 pm

The grey anodized color indicates that the fitting is an AC811 aluminum fitting. The AC fittings are found on WWII aircraft and earlier aircraft. The AC fittings in the following photos are from a hydraulic component that was installed in a B-24.

In the first image examples of a grey anodized aluminum AC nut and (plated) brass sleeve with the more common blue anodized aluminum AN nut and sleeve are shown. The parts are similar and serve the same purpose, but do not mix.

The second image shows an AC811 nipple fitting with an AN816 nipple fitting. Both types require flared tubes with sleeves and nuts, but will only work with the same AC or AN fitting, not mixed in the size that is shown.

Fri Jan 02, 2009 11:44 pm

That's a negative ghost rider, I can guarantee that the fitting I put up before is an AN818-6D fitting. If I remember right, the thread pitch on an AC fitting is slightly different (which I just verified in the shop,) allowing AN's and AC's to be interchanged up to a -4 size (the -4 maybe wrong, but I came across the issue on a B-25 and that is what I think my research showed many years ago.) My question, which I think Chuck answered, was when did the military changed from Clear anodize to blue anodize. There is a transition in there where a brass sleeve was used with a blue anodize. The follow up question would be; Did that occur during WWII or after. If I can use the NOS Fuel lines I have, than that would save time. If not, than I have to re-anodize the fittings and make new lines.


Fri Jan 02, 2009 11:47 pm

Nice AC fittings though, whose B-24 are they out of?

Fri Jan 02, 2009 11:49 pm

You can mix some of the parts. You can use an AC sleve with an AN819 Nut.
You can also use an AN819 nut on an AC811 nipple( or other AC threads). You can NOT do it the other way, AC nut on ANxxx thread for example. The AC fitting will not tighten down on the AN threads.
Its also not a 100% given that only AC fittings are grey colored. I have seen very early grey AN parts with my own eyes.
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