Bolts Headmarks & picking my battles!

[Jeff B.]

I'm in the middle of my first complete restoration and I'm having a great time with it. While I want to have it Flight Judged I have already made some decisions that I know will cost points. This is mainly in the area of over-restoration of the body and frame. So I'm trying to keep track of the points I'm knowingly giving up. The judging manual does on give any indication as to the amount of points incorrect headmarking will cost. This is a confusing area. Some of my bolt sets that seem original are not even matched sets. My differential to cross member bolts for instance have two different headmarkings. This same is true for the exhaust manifold bolts. At this point, matched sets of reproductions are looking good to me. Can anyone tell me a rough estimate of point loss for an incorrect bolt headmark?

[Terry M.]

Re: Bolts Headmarks & picking my battles!

It is not unusual to find one head mark on one side of the car or engine and a different head mark on the other side. There were sometimes different workers on each side of the unit, with different bins of fasteners which sometimes had different head marks.

I am always more suspicious of the fasteners when ALL the head marks are the same than I am when they are different.

[Chuck S.]

Re: Bolts Headmarks & picking my battles!

...I am always more suspicious of the fasteners when ALL the head marks are the same than I am when they are different.

Indeed.

Trying to get all your headmarks the same would be OCD behavior never experienced by the GM assembly worker of the period. It would be the highest level of over-restoration. The odds of having all matching head marks, even in an area worked by the same two man assembly team, are VERY long.

If you had been highly observant when you removed your fasteners, you would have discovered that order can be observed in apparent chaos if you look close enough.

Fasteners of a given head stamp ARE likely to be grouped together in one assembly area, say suspension, on one side of the car, with the possibility of an "out layer" or two. The opposite side of the vehicle may have a different headstamp for the same fasteners, but again all grouped together, and maybe with singularities of another headstamp. The common feature of such fasteners will be size, finish, and type. Fasteners in the same assembly area with a different thread size, finish, or type are still likely to have a completely different headstamp.

Different headstamps, however, are less likely to be mixed willy-nilly, say half and half, on one side of a vehicle in a given assembly area.

[Peter L.]

Re: Bolts Headmarks & picking my battles!

Jeff - I agree with Terry. When you look at the head markings on identical application bolts on original cars, mixed head markings are in general the rule rather than the exception. So, if the bolts are identical as far as specification such as grade, length, etc. and you have no reason to think they are not "originals," I'd stick with them. That's not to say you don't find identical head markings for identical application bolts on original cars but you can guarantee you'll find them on replacement bolts from suppliers. Pete

[Gene M.]

Re: Bolts Headmarks & picking my battles!

If you are using "hardware store" bolts and not marked with known original mftg'ers markings. I would suggest a 10% to 20% deduction on the item secured with incorrect hardware.

[Michael G.]

Re: Bolts Headmarks & picking my battles!

Bolts used throughout GM assembly plants were typically sourced to more than one supplier, so it was very common to find different head markings for the same part on one car. It was also normal procedure for line workers to dump new parts from one box in with older parts remaining in the bottom of a bin (or box) from which they were working. This means that, over time, the same bin might have parts with two, three, or even four (I've seen this) head markings, possibly resulting in a worker who installed a part in two attachments (right next to each other) using two different head marking on the same component.

Additionally, workers sometimes substituted wildly different parts (ie pan head for hex) temporarily when supplies of the specified part were extinguished, just so they could continue production. I'd say that if a similar the part was in the assembly plant when your car was built, it had a chance of making it on your car. Also, head markings from known GM suppliers could be on any part.

What you should be concerned about is parts with no mark on the head or parts with only the steel class markings. Those wouldn't have been factory installed on your car.

[Jeff B.]

Re: Bolts Headmarks & picking my battles!

That's really good information, I think I have a better understanding now. So when a reproduction bolt manufacturer provides, say, a set of intake manifold bolts with "TR" headmark, would it be safe to say they are picking one of the known headmarks for this bolt? Also, what does the TR, UR, M ect. stand for? Is this the bolt suppliers logo?

[Jeff B.]

Re: Bolts Headmarks & picking my battles!

I have read all of the posts in this (my) thread along with every other thread in the archives that address bolt head markings. There are alot of valid points and opinions but one thing is for sure. Those of us that are restoring these cars are far more concerned with the bolt head markings than anyone who designed or build the original cars. The real trick is to try to reproduce the randomness of the production line, which is not really possible. Which takes you back to the first thing I was told when I joined NCRS. "It's only original once". But I guess if it was easy, everyone could do it!

[Chuck S.]

Re: Bolts Headmarks & picking my battles!

That's really good information, I think I have a better understanding now. So when a reproduction bolt manufacturer provides, say, a set of intake manifold bolts with "TR" headmark, would it be safe to say they are picking one of the known headmarks for this bolt? Also, what does the TR, UR, M ect. stand for? Is this the bolt suppliers logo?

Yes...the letters identify the manufacturer of the fastener.

Radial lines will identify the strength class of the fastener; e.g. three radial lines is Grade 5, six radial lines is Grade 8. I believe no radial lines is Grade 2, a low strength fastener used only in low load, non-essential applications like attaching splash guards, etc. The position and orientation of the radial lines probably means something specific according to the different manufacturers, but it would take more study of more fasteners for me to understand the system.

[Michael G.]

Re: Bolts Headmarks & picking my battles!

Each fastener manufacturer has a mark that they cold forge into the head with a die during the "heading" portion of the manufacturing process. Some manufacturers have several different marks. Today, these marks are required by the U.S. Fastener Quality act, but in the sixties they were required only by the purchaser (GM). There is a document available which lists all the marks and who they are associated with. If you wonder about a particular mark, I may be able to tell you off-hand whose it is (or was), but, if not, I can usually probably find it easily enough.

In regard to a particular mark, on a particular bolt, the reproduction company you bought it from may be duplicating the most common head marking found on a particular series of cars. This could be driven by NCRS "correctness" standards (I'm pretty new to NCRS, so I don't know this for sure).

Interestingly, according to the current law, as I understand it, the reproduction company cannot legally apply this mark to the parts they sell unless they had the parts made by the original manufacturer, or, in the case of extinct companies, have registered that mark themselves with the U.S. Patent and Trademark Office. (I'm not an attorney, though, so, take this with a grain of salt.) I hope that helps, Mike

[Michael G.]

Re: Bolts Headmarks & picking my battles!

two more notes and I'm done:

1) the only real purpose of the manufacturer's markings was to be able to identify the source in case a problem cropped up in production or in the field.

2) the strength "class" markings are standardized, they are described by GM, ANSI, and several other "Standards".

[Jeff B.]

Re: Bolts Headmarks & picking my battles!

The bolts I'm using as an example came from Corvette Central. And I would imagine you are correct that the reproduction bolts are driven by NCRS correctness standards or at least one that will pass. In many cases Corvette Central lists a bolt that is the correct hardness and size at one price and then a certain (I assume correct) headmark bolt for the same application for a higher price. When you are looking at a bunch of 45 year old crusty bolts going back into your megadollar project, the new bolts are really tempting. My retentive nature has me torn between original bolts that are in various states of decay and sorted headmarks, or new bolts in matching sets with the same (reproduced) headmark.

[Stephen B.]

Re: Bolts Headmarks & picking my battles!

Look into the option of having the originals replated. We've discussed bolt plating a few times on the forum. Perform a search, and you'll find lively discussion of home brew plating systems.

[Mike M.]

Re: Bolts Headmarks & picking my battles!

You bring up a good point, Jeff.
If a person is restoring a car needing any repop parts, be sure to state this and confirm the faithfulness of the part/s with the supplier.
Vendors typically offer parts that are functionally interchangeable but may be lacking in some or all of the typical judging areas of CCDIF.
HaND

[Alan D.]

Re: Bolts Headmarks & picking my battles!

Paragon has a nice Bolt Chart showing typical head markings for 53-67, use as a reference since its not all encompassing.