70 Rear Bumper Bolt Head Markings

[Juliet P.]

I'm ready to put the rear bumper & brackets back onto my '70 (#4102 B18) now that the minor bodywork is done. I was missing some bolts since the bumpers weren't properly attached when I purchased the car in Dec '99. I ordered the "correct head" rear bumper bolt kit from ZIP which came with 'A' and 3 radial bars on them. Some of the bolts I removed, bead-blasted & replated had a 'M' or 'W' and 3 radial bars on them. Some were not legible. I'm not 100% certain if the bolts I took off & restored are original or not. Which is correct, 'A' or 'M/W'? Is there a way to tell from the AIM? The JM discusses finish (cad plate vs. black oxide) but makes no mention of the head designation.

Also, is there a good source for the correct bolt head markings? Only thing I've ever seen in friends garages is in poster format (no wall space in my garage). Is something like this available in a book form? I didn't see anything listed in the NCRS reference books area. Thanks, Juliet


Juliet's 1970 Corvette

[Roberto L.]

Re: 70 Rear Bumper Bolt Head Markings

Paragon catalog have a good sample of head markings with what they know to be correct. I asume it is not perfect but it's a good guide to check as any other source. If you like I have scanned the pages just for my personal use, as a reference, so I could send you the files. But honestly living you there it is more convenient to ask for a Paragon catalog which is very good.

[Gary F. LeDuc]

Re: 70 Rear Bumper Bolt Head Markings

Your "M" head marks are also correct.....

[Patrick H.]

Re: 70 Rear Bumper Bolt Head Markings

Juliet,

Generally a variety of companies were supplying bolts at any one time, so several varieties of head markings would be considered correct, such as your M. That is why making a "correct" list for every car, year, option, etc. would be a huge undertaking.

Generally these fall under "judge's knowledge" area. The commonly accepted markings are known to many judges, and as long as you are close, you get credit. The aftermarket ones aren't necessarily a correct match for YOUR car, either. From Paragon, the kit for my 71 intake all had the same head marks. Originally, there were 4 (!) different head markings, depending on the location and function of the intake bolts. The originals are stored in my basement for reference.

Hope this helps,

Patrick

[Juliet P.]

Re: 70 Rear Bumper Bolt Head Markings

Thanks for the explanations & data references. I understand the different supplier angle, however were different batches ever mixed at the assembly level on one car? Or should all the bolts for a particular function (ie bumper brackets) be the same type? Is it possible or likely that both 'M' and 'A' bolts might have originally appeared on my corvette's rear bumper?

What I am going to do is to reinstall the (supposedly) original 'M' bolts into the locations from which they were removed. These bolts I have bead blasted and electroplated or black oxide coated as appropriate. The missing bolts I will install with the 'A' head markings from the Zip kit. I have opted for this approach since it uses more of the original parts on my car, instead of switching them all to a matched set of 'A' repro bolts. It might raise a flag with a judge somewhere who notices that the A bolts are very legible and new, whereas the M bolts look like they had 30 years of rust on them & were recently restored (which they were!) If 8 of the 10 bolts are original and only 2 are repros, I have to think that's better than 10 repro bolts, even if he repro ones do match and have the correct head marking for some cars.

In the meantime, I'll add two slightly used looking 'M' bumper bolts to my swap meet & junk yard shopping list. ~Juliet


Juliet's 1970 Corvette

[Wayne W.]

Re: 70 Rear Bumper Bolt Head Markings

Very possible, even likely.

[Jerry Clark]

Re: 70 Rear Bumper Bolt Head Markings

Hello Juliet:

As I understand the mix and match situation as the parts bin was depleted it may very well have been replenished with parts from a different supplier as the parts arrived from the various vendors.

jerry

[Gary F. LeDuc]

Re: 70 Rear Bumper Bolt Head Markings

I have seen many cars with a mixture as you propose.

[Patrick H.]

Re: 70 Rear Bumper Bolt Head Markings

Juliet,

As the others have said, absolutely. That's part of what I was getting at. If there are bumper bolts of different sizes, this would ESPECIALLY be true.

By mixing M and A, you're probably going to be more correct than all of one.

Patrick