[Milsurplus] BC-347-A Interphone question

[Hubert Miller]

I was looking at a new unissued, in original packing BC-347-A interphone amplifier.
Looking at the back side, I see in each of four corners, but not rigorously in the same exact position for each corner, a wire-sized hole.
The first time I noted this, on a used BC-347-A, I thought, aha, someone wanted to run wires into it, for a ham hack.
But this new one has the same.
What are these holes about ? They are ungrommeted, so any wire transiting would be abraded.
thanks-
Hue
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