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Bolt Replacement


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I will be replacing many bolts and nuts on the frame-off restoration of my 1947 pickup. To meet the AACA judging requirements how should I proceed? I would prefer to use grade 8 or grade 5 bolts for obvious reasons, but what about the bolt markings that these bolts (and other grades) carry. If I grind off the bolt markings, the coating will also be removed which would mean the bolt head would rust before I got the truck to the first show. To my knowledge, due to EPA regulations there are no cadmium plating facilities in the US available for small runs. Additionally, there is the question of the head height of the present day bolts verses the taller bolt heads that were used in years past. I have found availability of a few sizes of high head bolts, but not nearly enough sizes to complete my project. There are no replacement bolt packages available for my vehicle. My question comes down to two points: bolt markings and head height. What are your thoughts? Surely this has come up many times before, but using the Search feature I get no hits.

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bferg...Welcome to the AACA Forum.

This subject came up and was discussed extensively around Dec. 2002.

Two items that may help.

1-Below, I have pasted my Bolt Strength study results from 12/18/02 and Ron Barnett's (Ronbarn) response dated 12/19/02 directly related to your question.

2-If you want to see a miriad of past discussions concerning bolts on this Forum:

-click "Search" in the header of this page.

-Forum's to Search: "Tech Questions" on the left.

-Keyword: Bolts, In Subject & Body

-User Search: Leave blank

-Date Range: "Newer than 4 years, older than 1 week.

-click on "Submit"

Hope this helps,

Peter J.




This is going to be a "long" one folks. I will start, with due respect, to George Rohrbach, who, made the initial post/query. In decending order, I post direct/simple opinions of "old" bolts vs. "modern" manufacture. Afterwards, the technical findings of the study, again, in decending order.


--Go with Grade 8, or, other Tempered bolts and Nuts for replacement on steering, tie rods, etc. applications. Your sample of a 1920-30's era bolt failed convincingly compared to Grade 8 and the jh Tempered Bolt. As Bill Stoneberg posted, Grade 8, or, other good Tempered Bolt.

--85,000 p.s.i. is normally for internal pressures for pressure vessels. Brinnell Hardness, or, a Rockwell Scale reading is the question: Again, replace with a high Grade/Tempered bolt.

--Bolt Head Dimensions:

(Did not use a Stainless bolt, as I personally would not use them for steering applications)

Tempered Bolt: .532

Grade-8 Bolt: .534

George's Bolt: .539

--Brinnell Hardness of the Tempered jh Bolt tested was first: 327.5-344.5

Brinnell Hardness of the Grade-8 Bolt tested was second: 293.5-310.5

Brinnell Hardness of the 1920-30's Bolt tested as third: 258.0-271.0

--Torqued Shear Points of the 3:

Tempered jh Bolt: Withstood 200 ft. lbs.

Grade-8 Bolt: Withstood 200 ft. lbs.

George's Bolt: Sheared at 147 ft. lbs.

(These bolts were all bolted down into tool steel with the heads flush to the surface.)

--JB-ed posted: "the Head Size was reduced about the same time bolts were "Graded" and would it have any affect on strenth?" in so many words:

Not in my opinion. The measurements of George's bolt head (.539)to the lowest measurement, the Tempered Bolt (.532) is miniscule, although, we are not creating a Space Shuttle here. We are looking at a difference of .007. The millage of the coatings could be just the difference.

--De Soto Frank posted: "...TRW joints included grade-8 hardened bolts in lieu of rivets". THAT ALONE SHOULD TELL YOU SOMETHING WHEN REPLACING bolts ON SUCH A SAFETY ITEM. The study I found sure backs it up, folks.

--Now, the chemistery findings:

(NOTE: Copper I found to be "Residual", meaning, it was present in either re-cycled metal, and, passed along to the bolt when it was produced.

Moly (Molybdenum, Mo) The Grade-8 Bolt appears to have been intentionally inoculated with Mo with a reading of .20. The Tempered Bolt had .02 and George's Bolt had .00, so, they read as residual. THIS BACKS UP BILL'S AND FRANK'S INPUT, THAT, ONE SHOULD USE A HIGH GRADE. 8 IN THEIR EXPERIENCES.

Here we go:

Grade 8/ Tempered/ George's Sample

Carbon © .39 .40 .35

Silicon (Si) .21 .23 .16 (Look out, folks!!)

Phospherous (P) .008 .012 .007 (Low)

Sulphur (S) .012 .011 .024 (Air Quality back then??)

Manganese (Mn) .73 .69 .64

Nickel (Ni) .02 .02 .01 (Low)

Chrome (Cr) .99 .10 .09

Copper (Cu) .01 .01 .05 (ALL 3 RESIDUAL)

Molybdenum (Mo) .20 Intential .02 Residual .00 (Non-existent)

Magnesium (Mg) .00 .00 .00

--Bottom line, go with Bill Stoneberg and Frank's advise...Grade-8 for replacement.

--This is one of those posts you hate to "hit send" in the sense that the "Legal Beagles" could rear their heads, however, the study was done on ISO Certified Spectrometers, and, Gauges, all of which, have been Certified within 4 days. IT WAS PERFORMED TO HELP STEER HOBBYIST'S IN THE RIGHT DIRECTION CONCERNING SAFETY ITEMS.

"Sorry that the line items are not in columns...been a long day."

Regards, Peter J.


Peter J. Heizmann

1972 Triumph TR-6



Peter - very good explanation and interesting test results. I agree with conclusions. After a review of this thread for comments about "dressing" the head of the bolt. If the car is going to be shown in AACA the judges will certainly take deductions for dress mark Bolts on the '20s and '30s vehicles. However it is an easy process to file or grind the marks off the head. Use modern Bolts and dress the heads!



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As Peter stated there have been numerous discussions regarding plating your factory bolts so I would do a search on the form. Eastwood and others also offer plating kits that seem to do a fine job.

I send my stuff to a cadmium plater here locally however there are others around. I got two boxes of bolts and brackets done for approximately $150 or so a few years back. I would recommend cleaning them up yourself with a good wire wheel as the platers do get lazy.

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There are places in both the D/FW and Houston areas (and probably others?)that will do cad plating for you. They usually charge a $100 minimum and expect you to clean all that you want plated well before bringing it in. Both gold and siler cad are available.

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  • 3 weeks later...

on the plating of the bolts if you have a company tha tis doing thier own plateing like Fasten all or a local hardware company sometimes they will plate your bolts for you of course for s fee. I have used that crome paint with good results, if you do a good sanding and de greasing of theheads first the paint sticks very well. But if you want to do it yourself there are a few sites on line that tell you how to set up your own plating vats.

why not black oxide the parts insead of cad plating since cad plating is not an original part item . You can get Black oxide kits on line also or from MSC tool supply.

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