Finish of the nut GM#120368

[Gary B.]

I’ve read conflicting information about the finish of the nut GM#120368. The threads are 5/16-24, and the nut is 0.27” thick. There are four of those nuts for the four studs on the fan clutch to secure the clutch to the fan. Several people on the DB have said the nut is zinc, and I believe all the catalog companies only sell a zinc version. But the ‘66 JG says it’s plain. Since the studs on the fan clutch are dark, the lock washer is dark, and the fan is black, a zinc nut will stick out like a sore thumb if zinc is incorrect. Does anyone have access to an NOS example of GM 120368, or to the GM engineering specs to clear up the confusion?

Thanks,

Gary

PS: Four of those same nuts are the ones for the studs that attach the carburetor to the intake manifold.

PPS: One of those nuts is also used on the compressor on AC cars, at least in ‘66. It’s item 10 in this AIM sketch.

IMG_9706.jpg

[Gary B.]

Re: Finish of the nut GM#120368

All washers in the 12038X and 12039X part numbers series are zinc plated

All lock washers in the part number series 10332X are plain; and dark from heat treatment

Adding to those two supposition is this new one of mine:

All nuts in the series 12036X and 12037X are zinc plated.

Does anyone have any information that refutes any of those suppositions?

Gary

[Richard M.]

Re: Finish of the nut GM#120368

Gary, David Bartush may have data on these. Maybe send him a PM with a link to this thread.

Rich

[David B.]

Re: Finish of the nut GM#120368

Gary, 120368 is zinc Would be careful about any locked in formula, part numbers were randomly assigned. Your suppositions mentioned due fall in line.

[Gary B.]

Re: Finish of the nut GM#120368

Gary, David Bartush may have data on these. Maybe send him a PM with a link to this thread.

Rich

Rich,

Good idea. David beat me to it. Thanks David.

Gary

[Gary B.]

Re: Finish of the nut GM#120368

Gary, 120368 is zinc Would be careful about any locked in formula, part numbers were randomly assigned. Your suppositions mentioned due fall in line.

I assumed it was a bit risky to suggest a part number/finish formula. The idea that 1203xx items are zinc is from an old posting by Joe Lucia. The idea that 103319-193330 lock washers are all dark, plain is something that I have found to be true based on as many of those 11 parts numbers that I’ve seen as NOS items, or have been confirmed by you from the GM engn drawings.

Gary