quote"That box has 9.8 cu.

Three for the wires on a dead end circuit, two or the outlet. lets skip the clamps.

5 x 2.25 = 11.25

I don't think that that box is code compliant for electrical. The ul listing is probably for phone or tv"

Good observation. I gave the wrong box catalog number. The right one is # 5070. 14.0 cubic inches. It has no clamps