It seems like there has to be new answers to some questions or questions to old answer as to what actual thickness were the light weight A-990 fenders, doors and scooped hoods in 1965.
Gauge?
Thickness in thousands?

I ask because I have a pair of supposedly A-990 fenders that even though are flimsy and lighter on the outer skins with standard inner framing, have a questionable thickness to them in thousands. Theory is that these things were stamped at different times in the built schedule and tooling, stampings may have varied from one to the other. Absolutely no signs of chemical milling though.

I've always heard that they were acid-dipped because stamping a lighter gauge steel would require expensive dedicated dies for a limited production run. Some sources say the final thickness was .018" (equivalent to 26 gauge).

I believe as the OP stated the sheet metal was stamped out in lighter gauge metal. Similar to how the front sheet metal was stamped from aluminum in 1964. I think the acid dipping part is an urban legend type thing that got started and took off from there. There are conflicting stories depending on what you read so I am unsure of a definitive answer.
I have Jim Schild's 1965 ramcharger book at home from when we had our 65 A990 coronet. So I will look through it when I get a few minutes. Our car had the original front fenders, doors, grill, glass, and bumpers, but the hood had been blown off at the track. We did get the hood but it was pretty well shot at that point from being left outside after being blown off. I saw no corrosion issues to any of the front fenders or doors normally related to acid dipping in the seems.
Only lighter thinner sheet metal like it had been stamped out that way.
Here is a prime example of conflicting stories of how the sheet metal was made. I pulled from an article of mopar muscle on the interweb.

The NHRA officials had gotten wise to many of the tricks used by the professional racers. Author of The 1965 Dodge and Plymouth Hemi Super Stock Authenticity Guide, Jim Schild tated, "Chrysler's answer to this challenge created some of the most important factory drag race cars ever produced. Late in 1964, production began on the '65 Race Hemi package cars with sale codes of W01 for Dodge and R01 for Plymouth." (On a side note, automotive historians debate over the original coding suffix, between 051 and 01. Historical sources we have found show the 051 code is considered correct by Chrysler's documents.) the '65 factory race cars were completely finished, purpose-built, full-size automobiles built expressly for winning at the drag strip. In lieu of the previously used plastic windows, special chemically-tempered lightweight Corning glass was used in 1965. The rear quarter windows were fixed, thus eliminating the window regulators. Since the NHRA expelled the use of aluminum body panels, Chrysler opted to build the fenders, hood, scoop, and doors out of 0.018-inch steel. The front bumper was made from slightly heavier metal, but, nonetheless, was light. Other reports record bare materials were chemically milled and acid dipped. This eventually became one of the tricks that professional racers used, as well as the factory when they built the altered-wheel-base cars

Matt

I have certain chemically milled (Acid dipped) parts that I had milled myself and there are obvious signs of the chemically milled process.
Plus, usual other adverse signs of Acid bath is the corrosion in untreated areas and especially uneven surface matter at the edges and seams unless they were treated and this new treatment is a recent trend way after the 60's and 70's.
The treatment in recent acid bathing practices is the application of special coatings to areas not to be milled. This process creates a continental shelf of sought or drop edge between the acid area and neutral zone. These fenders do not have that signature anywhere, but are thinner by a large contrast. I ask because a friend said that they were originally 18 thousands thickness and my measurements are 26 or so thousands. Maybe he was meaning 26 thousands which equates to more or less .18 gauge IIRC.
I've also learned that gauge or thousands readings are different between many metals like stainless, galvanized and regular steel.
I'm confused at the moment to be honest.

My 1965 parts book shows two different part numbers on the 65 fenders.
Part numbers specific to the A990 cars, and part numbers for regular fenders. So to me that would make sense to have been made from different thickness sheet metal.
The regular part numbers are 2525856 and 2525857 for plymouth.
A990 plymouth fenders 2416885 2416886.
Dodge regular fenders are 2525858 and 2525859
Dodge A990 fenders are RT 2416888 LT 2416887.
The A990 part numbers are also backed up in Jim Schilds 1965 Dodge and Plymouth Super stock Authenticity guide.
Also from Jim's book and I am quoting
"the doors were identical for dodge and plymouth.
The super stock door shells were lightweight steel and carried part numbers 2416889 for the right and 2416890 for the left. Most era literature states that these doors and the other lightweight body panels were built and then acid-dipped or chemically milled to remove metal thickness. Chrysler Corporation Product Planning,Technical Section, Fleet Engineering Detail Instructions (A-105,ARAP 5030, dated September 22,1964) indicate that these parts were to be stamped from 0.018-inch thickness steel which would have required modifications to the stamping process as the presses are designed for a specific metal thickness. It is possible that the lightweight parts were made both ways depending upon when they were manufactured but existing lightweight body panels were measured and they are 0.024-inch thickand the parts did appear to have been dipped."
Other details for the lightweight sheet metal is the LT door has no mounting holes for an outside mirror.
The front fenders will only have holes for the coronet badge. The right side part number 2416888 will also have the standard small gold pentastar emblem. There should be no radio antenna hole that might normally be found on a stock fender.
Matt

Picture from Jim's book.

from book picture #2

Mathew,
You may be giving my argument some legs with the pictures and literature in Jim's books but also opening a supreme court debate on the details of these rare items of yore. I also have those books by the way.
I just found it confusing that it was stating that they were stamped from 0.018 thickness and then.....("But existing lightweight body panels were measured and they are 0.024-inch thick and the parts appear to have been dipped")
From what my friend just told me, my fenders were reading in the .026-27 thickness range which equates to 23 gauge in translation. These readings were at the fenders ends and not in the middle as the micrometer could not reach its arm that far. The inner frame work that supports the outer panels and mounting points appeared to be of standard thickness. This may have been to keep some structural strength. If there was any chemical milling involved, then those inner frames would have been thinner as well.
That being said, is there a case now that only the outer finish panels were the items stamped out of thinner gauge being that fenders of the time were a multiple of different parts spot welded and folded together and into each other?

My fenders by the way had all the preexisting colors of the real A-990 cars that they were mounted on before as I was stripping them a few months back. The Passenger fender has no antenna hole or any signs of it being plugged and welded, even professionally. Though, my friend has also stated that regular production cars with radio delete may had come with no antenna holes as well on their fenders. This could be questionable and be a smoking gun.

Thank you by the way for your continued input.

Are part numbers stamped somewhere on these Ltwt fenders? I was also told that they may have not stamped them being that there were only a couple of hundred pairs and not for regular production runs.
Mine only seem to show NM 37-1 and NM 38-1 IIRC.

I am not sure we will ever have a true definitive answer on how they were made. I can say that from my point of view from looking at the car we owned, I believe they were just stamped out of lightweight sheet metal. The reason that I say that is for a car to have been 45 plus years old when we owend it, it had no corrosion issues in the seams that are normally related with cars/ parts that have been acid dipped. I hope some of this may have helped.
Matt

True this as these fenders I have are absolutely super clean, even cleaner than regular production fenders that I have seen in the past. No corrosion anywhere behind or in between.
A little smoking gun may be also evident on the one small tabs on each fenders wheel wells that hold the inner firewall splash panels. Depending on where and how they are mounted, there should be some witness type impressions of mounting bolts for the regular fenders and none at all for the A-990's.
My paint and body guy has joked that when he is passing his hand in the sanding process, he can feel it on the other side like there is only paper between them. LOL.

true, I forgot about the ink/paint part numbers.

Found out some interesting facts along with some mysteries and theories.
It just may be that even though the factory memo sheets that went out to NHRA depicting the exact thickness of the sheet metal may not have fallen into place after all like written.
Even though those memo sheets read off as .018 in thousands thickness, it seems that both NOS and used fenders from credible sources have read anywhere in the ballpark figure of .024-.027 in thousands thickness. Stock would be .038-.040
My friend Special K, thinks that a first batch or at least a first one of one stamping of the the sheet metal in .018 thousands may have resulted in very flimsy material at high speeds.
In contrast, the inner support braces may read anywhere from .035-.045 in thousands thickness. Stock would be .050.
Though some of these NOS pieces may have been dipped, they seem to have ended at the same thickness of my fenders which show no signs at all of dipping, Just thin slender fenders.
There was surely some funny stuff happening behind those factory doors way before the funny was put into those first Funny cars of yore.

I remember a incident at the 1974 or 1975(CRS disease) NHRA World Finals at Ontario raceway in Ontario,CA involving Steve Bagwells 1965 Plymouth A990 car drivers door, it seems some spectator thought there was a piece of trash stuck on one of the gold leaf letters on the drivers door and tried to pick it off, it was corrosion from the inside, not trash and that guy, person ended up sticking thier finger through the door skin I idn't see it happen, I did overhear it from some other Mopar racers in the pits that night while loading our car. I believe that was the same race that Dave Boertman didn't qualify for and ended up doing a burnout behind his trailer in the dirt from the frustration of not qualifiying, he ended up breaking the windshield out of another SS racer 1969 Nova pitted across the way from a flying rock from his burnout Not a good weekend for us Mopar racer, we didn't qualify in stock either The Nova racer, Bobby Warren, won the World Champinopship that year the next day

I know someone that is helping to restore one of Landys altered wheelbase cars...they want it restored exactly the way Landy had it set up...
They have found out that the roof skin is not the same as a standard vehicle as well..Supposedly its two sheets of metal that were much thinner pressed together rather than a single skin that came on the average car..

hey lee, what's the difference in weight of steel fender to a dipped one, lbs. ozs.?

The difference can be in the amount of dipping that the piece suffers through.
In other words, these days, the dipper can choose to leave the part bathing for a short period of time and remove only a small amount of material hence maybe if any, a couple of pounds.
The guy that I use takes the time and patience to bathe the part according to what I dictate to him.
Example, my bare dash frame weighed 17 pounds stock. I said that I only wanted to remove a portion equal to just before half its weight and not at all in certain critical areas of course for strength. The dipper removed just enough based on timing to remove 7 Lbs total and the critical mounting areas were left intact. The Dash weighs 10 Lbs now.
The part has to be super clean and rust free or else, the solution will continue to enhance the rusted area and possibly destroy the part like you see in an episode of The Munsters. LOL.

Some fenders are kind of light right from the get-go, so dipping may not be so necessary other than just removing the undercoating and years of various paint jobs. One paint job alone under another along with lazy body work can weigh as much as 3 Lbs or more. Ask me how I know.

And the difference in weight in my case from stock gauge to Super Stock gauge may be 10-12 Lbs per fender only IIRC.
I'll have to go to the scales again to put a light on the subject.

Hi , I saw your conversations regarding A990 fender thickness , I have a pair of the plymouth fenders that I've had stored in my basement for ages and will never use , I Mic'ed them after seeing your post and on the areas the mic's would fit they were .015-.016 and they have been striped of paint , my 65 is an old match bash car I brought back to life after sitting over at my farm in eastern Kansas for many moons , knowing the value of the fenders and given that I really use the car I put different fenders on the car and might sell the A990's here at some point ,
Jim Henry
MATCH BASH 65
Wichita,Ks.