66/67 AIM hole diameter question

[Donald H.]

I'm helping a friend get some rivets back in place on his firewall and tunnel. The two clips are on UPC M20/M21/M22 sheet A4. Clips are item #5 part number 3788712. I don't think there is anything particular about the clips as they are used in a number of places on the firewall.

The question is about the associated note for both locations for the rivet hole. The notes read .32 DIA. HOLE. Unless I'm missing something, a .32 hole is slightly larger than 5/16" which is way to big for any rivet I've used on a 66 firewall.

Is the AIM wrong are am I missing something?

Thanks,

Don Harris

[Richard M.]

Re: 66/67 AIM hole diameter question

Don, I think the AIM is wrong. The 450622 rivet can't be 5/16". I recall them to be much smaller, probably 3/16" => 0.1875".
I looked for the 450622 rivet diameter size in my records but no luck.

The same clip, 3788712, is used along the cowl for the hood cable so I looked at that page.... UPC 12 A8 Item 22. The holes for those clip rivets is referenced at UPC 1 Bolt Weld A6. There, the holes are noted as drill size 0.191". This makes sense as it's slightly oversize for a 3/16" rivet.

Rich

[Robert W.]

Re: 66/67 AIM hole diameter question

For what its worth, Paragon lists PN 827K-25 as a GM 455622 rivet set that's 1/8 dia x 3/8. Looking at that clip on my '66 w/M20, it appears to be a standard small sized rivet, not a large 5/16 dia. -Bob

[Richard M.]

Re: 66/67 AIM hole diameter question

For what its worth, Paragon lists PN 827K-25 as a GM 455622 rivet set that's 1/8 dia x 3/8. Looking at that clip on my '66 w/M20, it appears to be a standard small sized rivet, not a large 5/16 dia. -Bob

Bob, Thanks for checking. I searched here for the 3788712 clip and it states 1/8" rivet. Here are some related posts....

https://www.forums.ncrs.org/showthread.php?51475-C2-wire-clips&highlight=3788712

https://www.forums.ncrs.org/showthread.php?92315-New-Forward-Wiring-Harness&highlight=3788712

https://www.forums.ncrs.org/showthread.php?96505-C2-Splash-Shield-Floor-Pan-Attachment-Bracket-Finish&highlight=3788712

[Donald H.]

Re: 66/67 AIM hole diameter question

This all begs another question. Why did GM use decimal sizes to indicate what size holes to drill.

For example - the holes Rich referenced in the AIM as .191 diameter is a #11 drill in numeric drill index. However on the same AIM page there is reference to a .192/.199 DIA. I can't find anything that equates to .192. Numeric drill sizes #10=.1935, #9=.196 and #8-.199.

There is also a reference to a .140 DIA HOLE on the AIM page. The closes I can find to that is a #28 drill which is .1405 in diameter.

I wonder if the line worker used numberic drill bits vs more standard fractional drill bits? Or, did GM have custom drill bits for line workers to use.

Or, did the engineers just come up with odd sizes just to pxxx-off the line workers?

Thanks,
Don

[Richard M.]

Re: 66/67 AIM hole diameter question

This all begs another question. Why did GM use decimal sizes to indicate what size holes to drill.

For example - the holes Rich referenced in the AIM as .191 diameter is a #11 drill in numeric drill index. However on the same AIM page there is reference to a .192/.199 DIA. I can't find anything that equates to .192. Numeric drill sizes #10=.1935, #9=.196 and #8-.199.

There is also a reference to a .140 DIA HOLE on the AIM page. The closes I can find to that is a #28 drill which is .1405 in diameter.

I wonder if the line worker used numberic drill bits vs more standard fractional drill bits? Or, did GM have custom drill bits for line workers to use.

Or, did the engineers just come up with odd sizes just to pxxx-off the line workers?

Thanks,
Don

Don, Good question. I always had the same question about those unusual sizes.

Rich