Antique Aircraft Hardware

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!