I've been curious about this for a while. Does anyone here know how to interpret the casting "clock" symbols as shown below? I suspect it depicts a work-shift detail such as time/shift the particular part was poured. My guess is the smaller "external" dot (top of circle) represents "PM" and the larger dot (bottom of circle) represents "AM," making this one 11:00 AM. Any other ideas? These things are on every cast piece that I've noticed: intake, diff, exhaust, block, etc.The one below is on a runner on the intake manifold.



Your thoughts?

 

This is from the book Chevrolet Small-Block V-8 ID Guide, but I assume it applies to all GM castings. Middle of the RH column.

 

Thanks, Joe. So, I was on the right track, at least. Now I know more than when I started.

few minutes later:
I note that the Olds version has 12 dots in circle, rather than 10, as on the Chebbies. Also that the arrow indicator within the circle is not addressed in the Chebby book. I'll check out more of my parts and see what other differences are to be noted.

 

did you note the slot shaped notch in the pointer signifies night / day
well read the doctrine again and get back to me
Thanks