Bolt Grades

[Dan D.]

For our period correct fasteners, most bolts have the manufactures ident on the head. TR, WB1C, UR, etc. But there are no other markings to indicate what grade the bolt is. If there are no markings, am I to assume they are grade 2?

Dannnn

[Gary B.]

Re: Bolt Grades

Dan,

Here is a chart of bolt grades. Typically we only see Grades 2, 5 and 8 on our Corvettes.

C38A6782-BCD0-4C11-8DBE-E093650892A3.jpg

This 2nd chart gives the grades which are often cited on GM engineering prints; courtesy of Dr. Rebuild.

159E5166-CD38-45FD-A7A7-0D41DD00FC7D.jpg

[Mike B.]

Re: Bolt Grades

Dan,

The only Grade 290 bolt with 5 lines that was ever found on my '66 427 is the harmonic balancer to crank bolt. It's head mark is "F-C." I know it's original to my car since a good buddy's '66 427 has this same bolt on his car. 600 cars after mine. Other NCRS members have reported this bolt on '65 396 engine cranks.

As Gary stated, the majority of the bolt grades found on my car were 2, 5 and 8. Some also show as grade 5.1. Grade 6 bolts are found on the engine block and heads.

Mike
Harmonic Balancer Bolt & Washer (1).jpgHarmonic Balancer Bolt & Washer (2).jpgHarmonic Balancer Bolt & Washer (3).jpg

[Joe L.]

Re: Bolt Grades

Dan,

Here is a chart of bolt grades. Typically we only see Grades 2, 5 and 8 on our Corvettes.

[ATTACH=CONFIG]111583[/ATTACH]

This 2nd chart gives the grades which are often cited on GM engineering prints; courtesy of Dr. Rebuild.

[ATTACH=CONFIG]111584[/ATTACH]


Maybe our Corvettes have a few grade 290 bolts with five lines, but I don’t know what they would be. Others will know.

Gary

Gary------


The rear spring end bolts are GM-290M.

Most if not all, SEMS bolts, usually 5/16 or 3/8 with pointed tip and captured lockwasher, are grade 5.1

[Gary B.]

[Michael G.]

Re: Bolt Grades

If you're using repro bolts, pay no attention to the grade markings, most foreign manufacturers don't have a clue about non-metric markings, and probably wouldn't care if they did. High carbon steel and heat-treatment both cost money.

[Gary B.]

[Dan D.]

Re: Bolt Grades

Thanks for all the good responses guys. I have learned some things in reading your posts. And Mike, I hear you regarding the off-shore hardware you see in places like Loews and HD. They look like a million bucks with the bright zinc plating, but I often wonder about the heat treating and annealing that drives out the hydrogen. I got burned about 10 years ago with one of these bolts that I think suffered from Hydrogen enbrittlement. It was in a non-automotive application, and no damage was done.

But my question is about our old original equipment bolts that have only the manufactures identification markings. Would they be grade 2? I would think the controlling drawing would have this information. I am using these bolts where possible, but the strength determines the application I use them in, and what I torque them to.

Dannnn

[Michael G.]

Re: Bolt Grades

If it’s made in the U.S.A and carries the manufacturer’s own head marking (whatever that is), the chances are probably 100% that the part meets the specs on the head. I don’t know what AMK makes, so I can’t comment on them particularly.

I doubt a U.S.A. manufactured part is ever labeled deliberately wrong, strength-wise, by anyone. Foreign-made, without the actual manufacturer’s head marking (ie: with duplicate “reproduction” head markings), all bets are off.

I could tell you horror stories about what was being shipped into the U.S., and the calamities that befell the users, before the Fastener Act was enacted in the 90’s. That was supposed to end the problems, but you can (and people do) drive semis full of parts around the many exceptions.

I’d never use a foreign-made repro part without the actual manufacturers head marking in a critical application - even then you’re taking a chance it was shipped to the U.S. by a fly-by-night, single-desk, Chinese importer who’ll disappear overnight if someone gets killed.

If I can restore an old part, I always do it. But I’m just an old fastening engineer.

Dan, the GM fastener drawing would have carried the GM material spec number, you’d have to refer to the actual specification page in their Standards of the time to get actual strength information.

[Gary B.]

Re: Bolt Grades

?..But my question is about our old original equipment bolts that have only the manufactures identification markings. Would they be grade 2? I would think the controlling drawing would have this information. I am using these bolts where possible, but the strength determines the application I use them in, and what I torque them to.

Dannnn

[Joe L.]

Re: Bolt Grades

If you're using repro bolts, pay no attention to the grade markings, most foreign manufacturers don't have a clue about non-metric markings, and probably wouldn't care if they did. High carbon steel and heat-treatment both cost money.

Mike------


I've been saying this for a very long time. The very last fasteners I want to use are the "reproduction" variety. When "reproduction" fastener manufacturers are allowed to use another manufacturer's headmarking, it's tantamount to allowing counterfeiting. I'd rather use hardware store fasteners. While the headmarking might not be "correct", at least it identifies the actual manufacturer and, in doing so, gives them incentive to make the part correctly. Too often in the "reproduction" industry, it's "form over function".

[Dan D.]

Re: Bolt Grades

The manufacturer’s trademark has nothing to do with the strength or grade. The grade and strength are determined by the number/arrangement of lines. The trademark could be from any manufacturer. For example, a Gr 5 bolt on a C2 might have come from any of three or four manufacturers, with three or four different trademark logos, but all would have three lines. And yes, if a bolt has just a trademark and no lines, then it would be Gr 2.

Gary

I understand that the trademark has no relationship to grade or strength. Its just that the majority of our old fasteners have TMs, but no lines, so the question is 'what are they'. You have answered my question when you say grade 2, which is what I suspected. Thank You.

If someone with access to the old GM drawings could confirm that, then it would be concrete evidence to the fact.

I have some comments about fastener torque too, I am going to start a new thread for this subject.

Dannnn

[Gary C.]

Re: Bolt Grades

Dan,

You'd have to find some who had the GM Engineering Standards books, which list the info you're seeking. Attempted to buy/pay for copies of those books for years, but no joy.

Am lucky to have a copy of 2 pages - see attached.

Gary
....

Hexagon Bolt - GM Engineering Standards.jpg Hexagon Bolt Chart - GM Engineering Standards.jpg GM Engineering Standards Fasteners book cover.jpg

[Gary B.]

Re: Bolt Grades

[Michael G.]

Re: Bolt Grades

The manufacturers mark does not itself specify a strength, but it is all important in ensuring that the bolt is actually made to the the strength class marked on the head. No manufacturer’s mark, no traceability, no promises. Old manufacturers marks, from now-extinct fastener manufacturers mean nothing. Beware.