Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bracket

[Scott S.]

The subject car is a 1967 small block (L79) with C60 (i.e., one regular LH horn mount, different RH horn mount)

Question: What are the correct Dimensions, Headmark, Grade and Head Type (indented or regular hex) for GM bolt # 3848408?


This bolt is used to secure the Horns to the Radiator Support and also used on the small block starter motor brace (1967 only). Bolt 3848408 appears to be a production-only part number. TDB archive search only turns up two Threads containing this part number, but neither was conclusive regarding Hex-head type (regular hex or indented hex), headmarks, grade or measurements.1967 AIM:

1968 AIM: Bracket

1969 AIM:

[John C.]

Re: Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bra

Scott

Attached is a photo of the 3848408 bolts that have on my 68 in the locations you describe. They are all the same. It is a little tough to see but it is and E inside a circle with 3 radial line spaced 90 degrees apart.

John

[David L.]

Re: Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bra

Scott,

According to my notes that I took in my 15-year frame up restoration of my 1966 Corvette the 3848408 bolt is 5/16"-18 X 1/2" and used on UPC 12, sheet A5 (horn). As I remember the it has an indented head and I believe that the end might be pointed.

The 122007 bolt has a regular hex head and was used on UPC 8, sheet A3, UPC-11-13, sheets A4 & A5, and UPC 12, sheet A4. I have the size as 5/16"-18 X 3/4" with a ? in my notes.

Dave

[Scott S.]

Re: Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bra

Scott

Attached is a photo of the 3848408 bolts that have on my 68 in the locations you describe. They are all the same. It is a little tough to see but it is and E inside a circle with 3 radial line spaced 90 degrees apart.

John

John,

I would normally call a bolt with three lines Grade 5, but I think Joe Lucia has mentioned in the archives that when the three lines are perpendicular and intersect (like a "+" with one "leg" missing) that this represents 275-M material, or slightly less strength than Grade 5 (280-M). With the "circle-E" headmark in the middle, connecting the three grade-lines (or obscuring where the lines might or might not have intersected), I don't know if that's a regular Grade 5 or the more unusual type that Joe described.

Either way, it's definitely not a Grade 2 bolt (no lines), and both yours and Dave's are indented Hex-type heads, so that's two parts of the puzzle resolved. Thanks very much for the post and the picture,

Scott

[Scott S.]

Re: Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bra

The 122007 bolt has a regular hex head and was used on UPC 8, sheet A3, UPC-11-13, sheets A4 & A5, and UPC 12, sheet A4. I have the size as 5/16"-18 X 3/4" with a ? in my notes.

Dave

Dave,

Thanks for checking. The AIMs (1966 & 1967, maybe others) both call out the 122007 bolt for the RH horn bolt for cars with C60, where the RH horn mounts to a plate on the inner fender, freeing up space for the Receiver/Drier, if I understand correctly. I am fairly confident that Bolt 122007 is Grade 2 and otherwise just as you described.

Scott,
According to my notes that I took in my 15-year frame up restoration of my 1966 Corvette the 3848408 bolt is 5/16"-18 X 1/2" and used on UPC 12, sheet A5 (horn). As I remember the it has an indented head and I believe that the end might be pointed.

About the 3848408 "regular" horn bolt, the plot thickens. I just did some more checking (I searched "bolts" this time instead of "bolt" ) and found multiple examples of midyear Corvette horn bolts on the usual auction website, offered by someone who ought to know these bolts. There are both Grade 2 (no lines) and Grade 5 examples shown. All appear to be 5/16-18 x 1/2", all with attached external tooth (square-tip) washers, and all with REGULAR hex-head (not recessed or indented). Grade 2 examples are shown with "TR" and "RBW" (two different styles) headmarks, and a Grade 5 "RSC" (like my starter motor brace bolt).

This same seller also has the INDENTED HEX horn bolts advertised as being correct for 1968-1976, with what the seller calls an "IM" headmark with attached external tooth washer (hard to tell the length of this one from the pictures due to viewing angle).

Is it possible that this bolt changed from a regular hex-head bolt to an indented hex-head bolt for 1968 production, without the part number changing?

[David L.]

Re: Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bra

Scott,

Back in the 1980's I collected a lot of horns from various mid to late 1960's Chevrolet model in the junk yards and as I remember the attaching bolts all had the indented head.
The markings would vary depending on the location of the the production line. When I get a chance I will go through my boxes of original Chevrolet & Corvette bolts as I usually tagged them.

Dave

[Scott S.]

Re: Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bra

Scott,

Back in the 1980's I collected a lot of horns from various mid to late 1960's Chevrolet model in the junk yards and as I remember the attaching bolts all had the indented head.
The markings would vary depending on the location of the the production line. When I get a chance I will go through my boxes of original Chevrolet & Corvette bolts as I usually tagged them.

Dave

Thanks Dave. It doesn't seem like a particularly obscure bolt, but the JGs don't reference the characteristics of this part directly, or in some cases, at all. That seems unusual for a fairly high visibility fastener, at least for 1968+.

[David L.]

Re: Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bra

Scott,
I am still looking for my box of bolts but I found these auctions on Ebay selling 63-67 horn bolts. I am surprised that the bolts are not gold plated for the price advertised.
Dave

http://cgi.ebay.com/ebaymotors/63-64-65-66-67-Corvette-Horn-Bolts-RSC-ORIGINAL-RARE-_W0QQcmdZViewItemQQhashZitem5643967db2QQitemZ370501123506QQptZVintageQ5fCarQ5fTruckQ5fPartsQ5fAccessories

http://cgi.ebay.com/ebaymotors/63-64-65-66-67-Corvette-Horn-Bolts-RBW-ORIGINAL-RARE-_W0QQcmdZViewItemQQhashZitem5643967d5dQQitemZ370501123421QQptZVintageQ5fCarQ5fTruckQ5fPartsQ5fAccessories

http://cgi.ebay.com/ebaymotors/63-64-65-66-67-Corvette-Horn-Bolts-TR-ORIGINAL-RARE-_W0QQcmdZViewItemQQhashZitem5643967d11QQitemZ370501123345QQptZVintageQ5fCarQ5fTruckQ5fPartsQ5fAccessories

http://cgi.ebay.com/ebaymotors/63-64-65-66-67-Corvette-Horn-Bolts-RBW-ORIGINAL-RARE-_W0QQcmdZViewItemQQhashZitem5643967d7eQQitemZ370501123454QQptZVintageQ5fCarQ5fTruckQ5fPartsQ5fAccessories

[Scott S.]

Re: Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bra

Scott,
I am still looking for my box of bolts but I found these auctions on Ebay selling 63-67 horn bolts. I am surprised that the bolts are not gold plated for the price advertised.
Dave

Yes, those are the same auctions I referenced in post #5 above. Judging by the color, I would guess they were platinum-plated, but I suppose it could be white gold

This same seller also has a pair of horn bolts listed for 1968+, and they match the configuration of the ignition coil bracket (same bolt part number) in the picture John posted above (post #2). Here is the link: 68-76 Corvette Horn Mount Bolts IM UNRESTORED SURVIVOR

So it seems the question remains. This bolt has the same GM part number (3848408) at the horn location in the 1966-1969 AIMs (and maybe the same through 1976), and the same GM part number at the ignition coil bracket beginning in 1968, as shown in John's picture. For 1966-67 it appears that the horn bolt should be a regular hex, Grade 2 or Grade 5, but it can't be both with one part number, can it? Then in 1968+ it changes to an indented hex Grade 5. But the part number remains the same...?

It seems unlikely that GM would change both the Grade of steel and the configuration without changing the part number. I am interested in learning about what happened in this situation, but ultimately I need to know what is correct for 1967, and then find one. Or two, if my starter motor brace bolt is incorrect. I only require one "regular" horn bolt, because of C60.

My hunch is that it should be a Grade 5, regular hex, based on the bolt that was on my starter motor brace (same part number as the horn bolt). But I don't know for sure if that is the original bolt on my starter motor brace, or not.

[David L.]

Re: Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bra

Scott,

I finally found the box of bolts.
I only had one original horn on my 1966 Corvette (Feb. 1966) and the 5/16"-18 X 1/2" regular hex bolt with the "RSC" marking and attached external tooth lock washer as shown in my photo is the original bolt. I buffed off the face of the bolt with my wire wheel to show the marking. When I bought my 1966 in 1979 it was painted red although it is now the correct color, Milano Maroon.

The 5/16"-18 X 3/4" indented hex bolt with "E" marking and blunt end with an attached 3/4" washer is from the headlamp opening brace rod BUT apparently it is NOT GM # 122007 (corrected 04/17/2011, 9:31 PM EST).

I have other 5/16"-18 indented hex bolts in my "collection" with the same "E" marking that have pointed ends.

Dave

[Scott S.]

Re: Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bra

Scott,

I finally found the box of bolts.
I only had one original horn on my 1966 Corvette (Feb. 1966) and the 5/16"-18 X 1/2" regular hex bolt with the "RSC" marking and attached external tooth lock washer as shown in my photo is the original bolt. I buffed off the face of the bolt with my wire wheel to show the marking. When I bought my 1966 in 1979 it was painted red although it is now the correct color, Milano Maroon.

The 5/16"-18 X 3/4" indented hex bolt with "E" marking and blunt end with an attached 3/4" washer is from the headlamp opening brace rod, GM # 122007.

I have other 5/16"-18 indented hex bolts in my "collection" with the same "E" marking that have pointed ends.

Dave

Dave, thanks very much for checking, more evidence in favor of regular hex Gr5 for 1966-67, then changing to indented hex for 1968+, but with no change in the GM part number.

About the 122007 Bolt, the 1967 AIM shows that same part number for the headlamp opening brace rod (UPC 12-A4, Item 4) as for your '66. I have found this bolt used in many places in '67, including the fan shroud, fan shroud extension, RH horn bolt for C60 and the muffler hangers, probably more. I have been under the impression that the 122007 is a regular hex head bolt, Grade 2, Cad or zinc, 5/16-18 x 3/4".

Is that not correct? Or is this another example of regular hex head bolts becoming indented hex head bolts and changing the grade of steel without changing the part number? This is hard enough without the fasteners impersonating one another

Attached is a picture of what (until now) I was confident were the correct GM 122007 bolts for my fan shroud (x4) and fan shroud extension (x2).

[Ronald L.]

Re: Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bra

Scott,

I don't agree this bolt was an indented head bolt and my originals are represented within what was discussed, RSC grade 5 specifically.

Nor do I agree that the part number would not have changed with a major revision - you'd have to show me the print.

As you have seen, the 122007 was used all over the place for 66 67 and I bet if you find unmolested cars, the originals will be in the support braces up in the head lamp pocket.

Its a PITA just to get a mirror in there to see what they are, and harder to change them, usually they don't get messed with unless someone has a reason to get in there like a front end hit.

They are RSC grade 3 zinc for 66 and I bet your 67 cars started out that way too. In my experience, it was a junk bolt that snapped easily and got replaced often. But, on cars that people did not want to restore, or had to get into, those RSC's are still there, and yes they are pricey right now...when you can find them. There is a way to get them made, but that won't change the price and if you get someone selling supposed blasted and replated bolts - they just might not be originals.

[David L.]

Re: Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bra

I have been under the impression that the 122007 is a regular hex head bolt, Grade 2, Cad or zinc, 5/16-18 x 3/4".

Is that not correct?

Scott,

You are correct. I believe that my photo of the 122007 bolt is not really a 122007 bolt but it was the one that I removed from my 1966. I just happen to find that bolt with a label as to where it came from. According to the notes that I made in my 1966 AIM I used bolt 9419402 as a substitute for all 122007 bolts when I did my restoration (1980-1995). I made the correction in my previous post.

After further research the 122007 bolt is a 5/16-18 X 3/4" regular hex head (see photo below).

Dave

[Scott S.]

Re: Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bra

Ron and Dave,

I have not found the GM 122007 bolt in the parts books covering midyears. The attached picture is from the 1954 GM Engineering Standards book, it's not easy to read but I have added red arrows pointing to GM # 122007. It's in the 5/16-18 column, and the 3/4" row. That row is labeled Cadmium or Zinc. The entire section is for hexagon bolts, 260-M steel (Grade 2).

It makes sense that this 122007 bolt would be found in the 1954 GM Engineering Standards book, because the Winter '84 (Vol. 10, #3) Corvette Restorer article titled "1953-57 Corvette Hood Adjustments" by Roy Braatz pictures and calls out bolt 122007 specifically.

I may not be correct, but this is the best information I can find so far on the 122007.

[Scott S.]

Re: Bolt #3848408 -1967 Horn AND Starter Motor Brace, 1968-1969 Horn AND Ign Coil Bra

Scott,

You are correct. I believe that my photo of the 122007 bolt is not really a 122007 bolt but it was the one that I removed from my 1966. I just happen to find that bolt with a label as to where it came from. According to the notes that I made in my 1966 AIM I used bolt 9419402 as a substitute for all 122007 bolts when I did my restoration (1980-1995). I made the correction in my previous post.

After further research the 122007 bolt is a 5/16-18 X 3/4" regular hex head (see photo below).

Dave

You beat me to it

When I started looking up information for the previous post, your most recent post hadn't shown up yet. I'm just not fast enough!