I occasionally get asked about the hardware I use on my restorations. If you are involved in aircraft restoration, this material will be familiar to you. If not, maybe you can pick up a few tips that will make your project stand out from others. Plus, I like to
make this blog educational as well as informative, so I thought I would do a
post on hardware as it relates to older aircraft. While I’m no expert or final authority on
this subject, I consider myself a perpetual student. I actually enjoy studying things like the
origin of the different types of hardware used on old airplanes. Yes, I’m a sick person! It’s all an effort, though, to make my
restorations as historically authentic as possible – and practical. I say practical because some things just
aren’t. As an example, I would love to
cover the Lincoln-Page with grade-A cotton IF it was available. But as we all know, decent cotton has not
been available for 20 years or more.
My
philosophy is that aircraft restorations should be done accurately in order to
preserve their historical significance.
But this is my philosophy. If you
want to replace all the hardware in your antique airplane with
phillips-head screws and modern hardware with a gold chromate finish, that is
your choice. Above all, you need to be
happy with your final product.
Now my disclaimer…what I’m listing are general
dates and findings that may slightly differ from your experiences. I use these general guidelines in my
restoration work and feel pretty confident in the historical accuracy. Occasionally, this knowledge has helped to
prove some EAA judges wrong with my findings – I’ll explain later.
The Army-Navy (AN) Standard
(now
referred to as the Air Force-Navy Standard)
We are fortunate
in the school I teach to have many volumes of all the AN and MS standards for
hardware. As far as I can tell, the
first AN standard started around 1926.
This seems possible, as a 1931 Nicholas Beazley catalog I have lists
both AN hardware and some “commercial” hardware available for purchase. My Lincoln-Page, built in 1928 also has this
early AN hardware. This early hardware
differed in a couple areas from what is available now. Bolts had no head markings like we all are
familiar with, and the plating was different.
I can’t tell you when the head markings started to appear, but I suspect
it was around the mid ‘30’s when hardware started to become even more
standardized.
The
original plating spec was QQ-P-416 Type I Class 3. Type I meant that it was plain cadmium
only. Class 3 meant a thickness of
.0002” minimum. This is the “silver cad”
that many restorers are familiar with.
The c
 |
| A batch of hardware I recently had stripped and re-plated |
urrent plating spec is QQ-P-416 Type II Class 3. The difference being Type II, which means the
hardware is coated with a gold colored chromate finish over the cad plating to
increase its corrosion resistance.
Unfortunately, this is all that can be purchased now unless surplus or
NOS hardware can be found – which occasionally it can. I will, like many restorers, strip and
re-plate the hardware with the “silver” Type I cad. Sometimes for a few pieces, I just remove the
gold chromate either chemically, or blast it off with non-abrasive walnut
shells in my bead blaster.
 |
| Comparison of Type II cad and Type I cad |
It appears
as I look at the standards, that the switch was made from Type I to Type II
around the mid ‘60’s. To complicate
things, though, not all the hardware standards were changed at the same
time. Keep in mind too, that inventory
levels would also delay the use of the new “gold” cad. This change in the plating spec ultimately
affected most all hardware – bolts, nuts, screws, turnbuckle ends, etc,
etc. So if you are restoring anything
built prior to the mid ‘60’s, you would be pretty safe in using Type I cad for
all your hardware.
Let’s look
specifically at some of the basic hardware…
AN3 thru AN20 bolts
 |
| Original 1928 AN hardware |
As I
mentioned, these original bolts had no head markings. Every bolt I removed from the Lincoln-Page
was like this. So to keep things
accurate, I worked with B&B Aircraft to supply me a large quantity of bolts
with raised markings on the head instead of those that are
embossed. This allowed me to remove the
head markings without compromising the head thickness. Of course this meant re-plating the hardware
even if it was Type I cad, since removing the marks exposed bare metal. The result is a rather insignificant detail
that many don’t take the time to do, but makes the aircraft more authentic. My students think I'm nuts for being this
picky!
 |
New hardware where I removed the head markings
and had them re-plated with Type I cad |
Nuts
 |
Examples of early nuts with Type I cad. AN 310 on
left, AN 320 in middle, and plain on right |
The most widely used early nuts were castle (AN 310 or AN 320 shear) and several types of plain nuts like the AN 315. The castle nuts looked a little bit different from what we have available now. I'll save and re-plate original ones when I find them. By the way, have you seen the price of castle nuts lately? Outrageous! I’ve seen these safety’d or
secured the conventional way with a cotter key, or the end of the bolt peened
over or punched with a center punch.
Lock nuts, like the familiar AN 364/365 did not start showing up until
the very early 1940’s – pehaps slightly earlier. This is where I had an interesting encounter
with an EAA judge. It was 1998, and I
was getting my Ryan PT-22 judged. The
judge informed me that he was deducting points because my aircraft had many AN
365 locknuts installed that weren’t available in 1942. Fortunately, I did my homework. I had the Ryan parts catalog that called out
the proper P/N, AN 365, and I had samples of original hardware that I removed
during the restoration. He didn’t know what
to say!
 |
AN 365 on left with Type II cad, AN 364 on right with
Type I cad |
Screws
 |
| Example of early screws |
Early
screws were either flat-head, round-head, or fillister. They were available mostly in steel and occasionally in brass. All were slotted. I see many antique aircraft with
phillips-head screws. Again, that is
your choice, but not authentic. The
phillips-head was patented in 1933. Auto
manufacturers started using it around 1937.
Some WWII aircraft were using the phillips-head during the ‘40’s. Because civilian aircraft production was shut
down during WWII, you won’t see this screw appearing on civilian aircraft until
after WWII. Even then, it may have been
years before they were used due to inventory levels. The 1946 Funk I recently finished had about 3
phillips-head screws on the entire aircraft!
 |
Phillips on left with Type II cad and slotted on right
with Type I cad |
Some folks also like to use stainless steel screws. Yes, they have corrosion resistance, but not authentic. I'm sure some stainless fasteners started showing up in certain applications on WWII aircraft, but in looking at the standards, it appears they didn't become more widely available until the early '60's. The dates here are sketchy, but if you apply the same rule as before: if it's prior to the 60's, don't use stainless
This may be
more than you ever cared to know about hardware, but it’s little details like
this that can set an aircraft apart from others. With competition tough at shows like EAA,
these are some of the things that could make the difference between that Silver
and Gold Lindy!
