Rear spring bolts.

[Larry Barickman]

In the process of replacing the side yokes on my 69 we had to cut the spring bolts. I orded a new set but they were back ordered. I had kept an old set(good condition) from re-doing a 71 a few years age. The bolts are identical except the 69's have grade 8 markings on the head (6 hash marks) but the one from the 71 have only four marks. The four hash marks are spaced exactly like the grade 8 configuration but with two marks in a row missing. Which is correct and are the ones with four marks safe to use?

[Larry Barickman]

amendment

I made a mistake in the last post. The grade 8 bolts have five hash marks.

[Joe L.]

Re: Rear spring bolts.

Larry-----

The original spring bolts used for both 1969 and 1971 (and most other years) were of the oddball "4 line variety". Later SERVICE bolts are of the 6 line (SAE grade type.

[Joe L.]

Correction

After reading you amendment, I recalled that my information was incorrect. The original 69 bolts (and I think most other year spring bolts) were of 5 LINE headmarking, NOT 4 line. However, 5 line is NOT SAE Grade 8. SAE grade 8 is 6 line. The 5 line is an oddball rating. I don't know why it was used. I think that all SERVICE spring end bolts are SAE grade 8.

[Larry Barickman]

Re: Correction

Joe... accoring to engineering books, five hash marks or six marks are grade 8. Grade five are three hash marks. Anything above three is an alloy.I cannot however find anything on four marks. These bolts also have a "Z" logo in the center of the head.

[Joe L.]

Re: Correction

Larry-----

In GM parlance, the "6 line" bolts are specified as meeting standard GM300-M. These are also, of course, known as SAE Grade 8. The "5 line" bolts are specified as meeting standard GM290-M. I was unaware that these were also known as SAE Grade 8, but that could well be the case. Perhaps, in the SAE rating system 2, 5 and 8 are the only choices. If so, 8 would be the closest. However, I expect that in the GM system the 300-M has a higher strength rating than the 290-M.

[Larry Barickman]

Re: Correction

Hi., Joe... I did a little reasearch last night as I hd never seen a four mark bolt. While I did not find a four mark rating per say I did find something interesting. Bolts with all of the marks in just half of the head diameter (as these I have),are made from martensite steel quenched and hardened. A martensite steel bolt with six marks is actually 8.2 on the sae scale. In reading about martensite steel it also said that they are much more corrosion resistant. I just thought you might like to know the piece of triva about hardware. Thanrs for the help.