No one would be able to use a wrench.
Someone should use a wrench on your head.....and tighten up the loose screws. ( Or a monkey wrench for tightening your nuts )
The heads of bolts, ( and the nuts) are measured ACROSS the flats of the head of the bolt.....IOW a bolt with a 3/4" head is designed so that the 3/4 inch wrench fits the flats of the bolt head.
But ....What the hell do wrenches have to do with the diameter of a carcano barrel??
But since you broached the subject...If you were to use the open end of the 11/16" (.687") wrench it would fit loosely around the carcano barrel .....If you use a metric open end wrench you'll find that the 16mm wrench will fit nicely around the barrel. And if you were to use that same 16mm wrench around a AA penlight battery you'll find that the battery is nearly the same size as the barrel of a carcano at the foregrip.