Thomas;

I think (think, mind you) this is part of the “stand” part of a mill stand, and the “clock” is the gauge by which the mill stand operator determined the thickness of the slab (billet/bloom), and whether or not to pass the slab back through, or not.  The rolls would be mounted in bearings in the two big openings.  It is not a mill shear, which looks like an extended c-clamp and has an opening in one end.

Just my opinion…..

Elden Gatwood