I am not sure your question was answered,
and I never looked at the IC flat specifically, but can speak
to another GSC cast flat often referred to as a “Commonwealth”
Keep in mind that castings varied by owner
and year built.
There were two kinds of “holes” in the deck
of the flat. The obvious ones were the square holes cast in
as stake pockets. Some cars had four at each end; these have
The other, more numerous “holes”, were,
from what I was told, “stress-relieving” depressions cast in
to minimize chances of cracking in the slowest-cooling portion
of the casting. There are obviously numerous circular
depressions in the surface of the casting inboard of the draft
gear and bolster.
The flats I crawled over had depressions
that did NOT go the entire depth of the casting. I could not
figure out a way they were used to secure loads, but I do not
know these cars. They collected a lot of dirt.
Some GSC cast flats did have tie-downs
welded to the side sill at the rim, in the form of steel
circles. See attached.
I cam across this photo of IC flats being assembled at the
IC's Centralia car shops from frames bought from General Steel
I've never seen these holes in the steel at each end of the
Maybe I've just missed them in other photos.
Jeff White Alma IL